408 



LERNEAD.E. 



LERNEAD^E. 



410 



deeper anatomical researches or investigations into their mode of life 

 and habits. Their true position however was soon about to be ascer- 

 taiued. Soon after Cuvier had published the first edition of his 

 celebrated work, the ' Regne Animal,' a French physician at Havre, 

 M. Surriray, made the important discovery that the ova were contained 

 in the long filaments suspended from the abdomen, and that the 

 young when born bore no resemblance to their parent, but on the 

 contrary were extremely similar to the young of the Cyclops. De 

 Blainville recorded the fact in the ' Journal de Physique,' 1822, in his 

 excellent article ' Lernea," and fully admitted the truth of Surriray's 

 statement. In this article he remarks the near approach of his last 

 genus among the Lerneadee to the last of the Caliyidte, and traced the 

 almost insensible gradations by which we are carried from that genus 

 to the Caligtu itself, thence to Argulus, and through it to the Apia 

 and other Branchiopods. He still retained them however amongst the 

 Epizoa ; and Desmarest, in his ' Cons. G6n. sur la Classe des Crust.,' 

 1825, appears to have been the first to distinctly refer them, as a 

 group, to the class Crustacea. 



In 1826 Messrs. Audonin and Milne-Edwards discovered a parasite 

 upon the Atacae, or lobster, the Nicothoe ; and in the course of their 

 observations upon the history of this curious Siphonostome they came 

 to the conclusion, reasoning from analogy, that the Lernex were real 

 Crtutac-'i that " became monstrous after they had fixed themselves" 

 upon the auimal which was to serve them with nourishment. 



Kroyer informs us that several German zoologists, as Nitsch, Leuc- 

 kart, and Schwegger, had advanced similar opinions, though it would 

 appear, from his leferences to their observations, upon very insuffi- 

 cient grounds. Zoologists however were gradually coming to the 

 conclusion that these fantastically-formed creatures were in reality 

 crustaceous. But it is to Alexander Von Nordmann, an eminent 

 Prussiau naturalist, that we are indebted for a complete and satisfac- 

 tory solution of our doubts upon the subject. In his work, ' Mikro- 

 graphische Beitrage zur Naturgeschichte der Wirbellosen Thiere,' 

 Berlin, 1832, he has confirmed the observations of Surriray upon the 

 young when first hatched from the ova, shown the dissimilarity which 

 exists between the male and female, and thrown much light upon the 

 anatomy of this interesting group of animals, especially with regard 

 to the structure of their mouth and feet. Since the publication of 

 his excellent work his observations have received still further con- 

 firmation, additions, and corrections by three zoologists of considerable 

 reputation the well-known entomologist Burmeister ; an Austrian 

 naturalist, Vincenz Kollar ; and the acute observer Rathke. 



The form of the animals belonging to the Lerneadee is very variable. 

 " Respecting this," says Kroyer, " it is not easy to say anything general. 

 The remark only forces itself upon every observer, that the exterior 

 of these animals is often so highly fantastical, that we are disposed 

 to admire the freaks of nature in bringing forth such forms. But it 

 is evident, that when continued observations and investigations have 

 put us in possession of the condition of these forms, we shall see here, 

 as everywhere else, that singularity resolves itself iuto regularity." 



For the most part the skin, or external envelope, is soft and flexible, 

 but there are many species in which it is somewhat of a cartilaginous 

 consistence. Nordmann has discovered that it consists of a threefold 

 structure ; an external layer, tolerably firm and elastic ; next, a very 

 loose and soft cellular tissue ; and finally, a third layer, composed of 

 a number of muscular fibres crossing each other in length and breadth, 

 and having in consequence a reticulated appearance. 



We can generally trace, more or less distinctly, a division of the body 

 into two parts ; the first of which, the smaller of the two, forms the 

 head, and the other the thorax. This latter is generally of consider- 

 able size, whilst the abdomen, in almost all the species, has become 

 Tery nearly rudimentary. Attached to the head, in the greater number 

 of the Lerneadee, we find one pair of antenna;, and two pairs of foot- 

 jaws, by means of which they attach themselves to their prey. In a 

 few we find no antennae, and only one pair of foot-jaws. We find no 

 appearance of eyes. The organs corresponding to the thoracic feet of 

 the tfipltonostoma are variable in form, but in general are almost 

 rudimentary, sometimes indeed altogether wanting. It is this very 

 rudimentary state of the organs of motion and other appendages that 

 forms the principal mark of distinction between the Lerneada! and the 

 Sijihonottoma. The mouth, according to Kroyer, has generally the 

 shape of a blunt spherical snout, placed on the most advanced portion 

 of the head, and terminating in a roundish opening, though in some 

 of the genera it is in the form of a slight elevation merely, and is 

 placed at a considerable distance from the anterior part of the head. 



The manner in which these animals fasten themselves to the fishes 

 upon which they live varies much. In some it is by means of the 

 foot-jaws alone, which in these species are strong and of a hooked 

 form. In others it is by means of two long appendages springing 

 frum the upper part of the thorax, one on each side, and uniting at 

 the tip, forming at their junction a sort of round button. In a third 

 get, again, the organs of attachment are a series of horux or appendages 

 proceeding from the side of the head. 



The females are generally furnished with large external ovaries, 

 containing numerous ova. The intestinal canal is very distinct, 

 extending through the whole body. It is cylindrical, and widens 

 towards the middle of its length into a stomach. The motion in 

 the living individuals may be plainly seen, a series of rhythmical 



movements to both sides, occurring to the number of from about 

 60 to 65 in the minute ; besides a sort of peristaltic motion, or an 

 alternate contracting and lengthening itself upwards and downwards. 



Nordmaun has described what he considers may be the liver and 

 brain, and has pointed out the heart. This latter organ contracts and 

 expands regularly, but no blood-vessels are to be seen, the blood flow- 

 ing freely about in the hollow of the body and arms. The blood is a 

 clear watery-like fluid, composed of three kinds of globules, differing 

 in form and dimensions. The internal ovaries lie on each side of the 

 intestinal canal, and open by means of a caualis deferens on each side 

 of the inferior portion of the thorax, where the external ovaries take 

 their origin. 



In general it is only the adult female of the Lerneadee that we are 

 in the habit of observing, and in an animal whose organs of motion 

 and perception for the most part are merely rudimentary, and whoso 

 existence is strictly stationary, the manner of life must be very simple. 

 Immoveably fixed upon the fish which serves it for food, its existence 

 depending upon the life of its host, it requires neither feet to transport 

 it from place to place, nor eyes to guide it in its search for fresh 

 abodes. In fact, the whole of its active existence consists in the two 

 operations of taking food, and propagating its species. We find them 

 in all instances more or less deeply fixed in the tissue of the parts 

 upon which they have taken up their habitation, and often so deeply 

 lodged, that little else but the oviferous tubes are visible externally. 

 There they remain, living at the expense of their host, those that 

 inhabit the branchiae or are deeply fixed in the soft tissue of the bodies, 

 drinking up the blood ; and the others which are fixed less deeply, 

 and take up their abode under the fins and such places, sucking the 

 slimy juices of the skin. As they are never seen to change their place 

 of residence, the question naturally occurs how did they come there 

 originally ? Having no feet to propel them through the water, and 

 no eyes to guide them, even if they possessed the faculty of transport- 

 ing themselves from one place to another, how is it that we thus 

 find them fixed upon these fishes, mature and possessing ova ? Blaiu- 

 ville answers this question by saving, " It is difficult to conceive how 

 these animals, which spring from eggs, are fixed upon fishes without 

 admitting that in their young age they possess a little motion." 

 M. Surriray had at that time demonstrated to Blainville the existence 

 of the young when just hatched ; but less importance was attached 

 to this discovery than it deserved; and it was not till Nordmaun 

 corroborated the fact, and followed it up by his more patient 

 researches, that we were enabled to answer the question fully. 



The circumstance that the Lerneadce soon die after being taken from 

 the fish that has served them for nourishment and a habitation, cer- 

 tainly throws great difficulty in our way of observing the development 

 of the young ; but we now know that when hatched, and for sorno 

 time afterwards, the young Lerneadte are nimble and active, and 

 possess both the organs of motion and the faculty of using them. 

 When they first come out of the egg they are of an oval shape, and 

 very much resemble the young of the Cyclopidce. They possess a 

 large eye, situated in the centre of the anterior and upper part of the 

 body, and are provided with two large pairs of swimming-feet, and a 

 pair of jointed antennae. As in the Cyelopidx, these young Lerneada: 

 cast their skin repeatedly before they arrive at maturity. After the 

 first moulting the body is seen plainly divided into two parts, the 

 anterior of which is furnished with three pairs of hooked feet, and 

 the posterior with two pairs of swiniming-feet. No doubt there are 

 a good many stages of development to go through before they assumo 

 the mature form, but it has not yet been possible to follow them out. 

 It is not the least curious part of the history of these singular- 

 looking animals that the young should thus stand on a higher stage 

 of development than the mother ; and that their progress from youth 

 to maturity should be in .the directly opposite ratio to that of all the 

 other Crutlacece, At what period of their existence they fasten them- 

 selves upon their prey is at present unknown ; but no sooner apparently 

 does this happen than the eye disappears, and the feet either disappear 

 also, or are transformed into other organs. In some they are changed 

 iuto foot-jaws, by means of which they fix themselves upon the body 

 of the fish they select for their habitation. In others they are trans- 

 formed into long and strong prolongations like arms, which unite 

 together either at the tips only, or from the roots all the way up to 

 the point, where they send forth a short horny stem, that widens into 

 the shape of a round button, and which, when buried in the skin or 

 Jesh of the fish, forms such a strong attachment, that the Lcrneadie 

 cannot be detached without beitig torn, or by being carefully dissected 

 out. Most probably the species in which this development takes place 

 irst fasten themselves to their foster-mother by the foot-jaws, as the 

 irst-mentioned set do, and after being buried in the flesh, these organs 

 assume this peculiar formation, otherwise it is difficult to conceive 

 low such an instrument could penetrate deeply into the body of the 

 ish. A third mode of transformation of the feet appears to be into 

 a series of horny branchlets developed round the mouth, and which, 

 when they have penetrated deeply into the soft parts of their host, 

 serve effectually to retain the parasite in its place. The adult 

 Lemeadve show, with the exception of taking food and laying eggs, 

 very few and feeble signs of life, whether attached to the nourishing 

 animal or when separated from it. Many of the genera show no 

 xternal signs of life at all after separation from their foater-inother; 



