So 



HARDWICKE'S SCIENCE-GOSSIP. 



Baldner, a self-taught naturalist (a fisherman) of 

 Strassburg, about 1700. In 1740, Frisch, in his 

 " Insecten in Deutschland," describes it as Fisch-laus. 

 Linnseus in his " Systema Naturse," mentions it as the 

 Monoculus foliaceus. The best description, however, 

 is given in " Ann. et Mus. d'Hist. Nat." for 1806, and 

 at the present time this article is largely quoted. The 

 Argulus was first noticed about fifty years after the 

 Caligulus, and several mistakes seem to have been 

 made, one author actually mistaking the tail for the 

 head. This was a pardonable blunder, as the use of 

 the microscope was little known in those days. It, 

 however, led to a great amount of confusion, as each 

 writer, copying the remarks of those before him, 



six layers of bronchial lamellae finely marked, and are 

 used for sucking the juices of the fish, or from the 

 mucous products secreted by the skin. Between 

 these suckers is a round sinus, whose functions I do 

 not know ; from near this opening commences the 

 alimentary canal, which runs through the centre of the 

 parasite, throwing off "coecal prolongations," and 

 terminating between the caudal appendages, where is 

 situated the cloaca. 



The primary canal contains the oesophagus, stomach, 

 and intestines. Below the sucking discs is a pair of 

 foot-jaws serrated in their inner edges, which are used 

 for masticating the food. In the centre of these jaws 

 is situated the mouth. Leydig describes the mouth 



Fig. 75. — Parasite of wrasse (ventral view) 

 i inch. 



Scale, 



Fig. 76. — Sucker of 



parasite of wrasse ; 



X 310. 



caused an accumulation of errors. Milne-Edwards' 

 " Hist. Nat. des Crus." gives a full and good descrip- 

 tion in 1840, and since that time several American 

 and Continental writers have greatly increased our 

 knowledge on the subject. 



The following is a description of two minute para- 

 sitic Crustacea which were taken from living specimens, 

 and which differ in some particulars from any hitherto 

 recorded. They give but a vague idea of the wonder- 

 ful organisation and beauty of form of these minute 

 beings, which are so perfectly adapted to perform all 

 the functions designed by Providence for these lowly 

 creatures. 



This parasite (fig. 75) is oval and slightly convexed. 

 It is divided into two parts, the thorax and the 

 abdomen ; the thorax coalesces with the hind part, 

 which is sometimes, but erroneously, called the tail. 

 The posterior part contains the swimming-legs. In 

 this individual the thorax is composed of a shelly 

 carapace strengthened by a series of bands diverging 

 from the centre. This shell extends to about three- 

 fourths of the length of the parasite. The remainder 

 consists of four segments of a soft sarcode interspersed 

 with small pink puncta. 



The last pair of segments has a distinct band which 

 serves to divide it transversely. A pair of sternal 

 forks is placed at the termination of the abdomen. 

 The cephalo-thorax is composed of a shelly trans- 

 parent substance, and according to Pickering and 

 Dana, is formed of two layers or substances. The 

 head is blunted and contains a pair of antennae, 

 which in some individuals is at right-angles, and in 

 others is turned upwards. Between these antennae 

 and the centre of the head is a pair of lunules or 

 sucking-discs (see fig. 76) which are composed of about 



Fig. 77. 



-Parasite of bass (ventral 

 view) ; X 25. 



in the Argulus foliaceus as follows : " The opening of 

 the mouth is placed in a club-shaped projection bent 

 downwards. It is divided posteriorly by a crescent- 

 shaped lower lip, anteriorly and laterally by two broad 

 gradually tapering plates, several disc-like pieces 

 inside representing the mandibles."* M. T. Thowell 

 observed " two small teeth." 



A little below the gullet is a pair of thoracic feet 

 graduating from the carapace to the termination, and 

 curved so as almost to meet at their extremities. 

 These legs are covered with a series of triangular 

 scales, which gives them the appearance of being 

 irregularly segmentated. Under these locomotive 

 appendages is another pair, much thinner and turned 

 towards the posterior. Between the shell and the 

 abdominal part is a pair of fan-shaped fins composed 

 of six cartilaginous ossicles and covered with a fine 

 membrane. These parasites have two simple oval 

 eyes. This Caligulus was taken from the Green 

 Wrasse {Labrus lineatus). Colour, opal white, with 

 dark crimson markings. Fig. 77 is an individual of 

 the genus Argulidse ; there are only two or three 

 species known. It is of a pale green colour and 

 about -jL inch each way, being nearly round. The 

 membranous carapace is covered with a peculiar 

 V-shaped marking, and forms a shield over the whole 

 of the body. The fore-part is obtusely round, it has 

 a pair of perfect eyes, very dark and brilliant ; 



* On the "Morphology of the Argulidae," 1866. 



