1033 



CHIUOCEPHALUS. 



CHIRONOMUS. 



1031 



Schoeffer discovered them in a pool of water near Ratisbon. Prevost 

 found his specimens at Montaubon, and at Jurine's request sent some 

 ova in moist paper to Geneva, where Jurine succeeded in hatching 

 them and making those observations which are published in his 

 'Monocles qui se trouvent a Geneve." Dr. Baird says, " It is rarely to be 

 met with in this country, compared with the Daphnice and many 

 other Entomoitraca ; the only place near London where I have met 

 with it being on Blackheath. They swim upon their backs, and in 

 fine warm weather, when the sun is not too strong, they may be seen 

 balancing themselves, as it were, near the surface by means of their 

 branchial feet, which are in constant motion. On the least disturb- 

 ance, however, they strike the water rapidly with their tail from right 

 to left, and dart away like a fish, and hasten to conceal themselves by 

 diving into the soft mud or amongst the weeds at the bottom of the 

 pool They are nearly transparent, and are of a very light reddish 

 colour, with a slight tinge of blue on some parts. ' When placed in 

 a glass of clear water,' says Prevost, ' the elegance of its form, the 

 ea.se and softness of its movements, its silvery transparency, or its 

 brilliant colours, its large black eyes, the small spot which it carries 

 on its head, the crown of the male are a beautiful sight, which the 

 most indifferent observer cannot see without pleasure." 



" It is certainly the most beautiful and elegant of all the Entomos- 

 traca. The male is especially beautiful. The uninterrupted undu- 

 latory wavy motion of its graceful branchial feet, slightly tinged as 

 they are with a light reddish hue, the brilliant mixture of transparent 

 bluish-green and bright-red of its prehensile antenna;, and its bright- 

 red tail, with the beautifully plumose setae springing from it, render 

 it really exceedingly attractive to the view, 



** The undulatory motion of its branchial feet serves another purpose 

 in addition to that of keeping the animal suspended in* the water. 

 The thorax or body of the animal has been described, when floating 

 on its back, as like the cavity of a little boat, the feet representing 

 oars. When them are in motion, they cause the water contained in 

 this boat-like cavity to be compressed, and to mount up as along a 

 canal, carrying in the current the particles destined for its food 

 towards tbe mouth. It seems to be constantly, when in this position, 

 employed in swallowing and digesting its food, its masticatory organs 

 being in perpetual motion. Shaw imagined this little creature to be 

 a fierce and voracious beast of prey, but it is not so ; he was misled 

 in so thinking by not understanding the true nature of its prehensile 

 antennae. These he imagined were organs for seizing its victims 

 and crushing them to death, though he candidly admits that he never 

 saw them attack other animals, and even says that he has seen them 

 succumb to the assaults of the C'yprii. According to Prevost, they 

 live upon dead animal or vegetable matter, but they have apparently 

 little taste, for they swallow every sort of thing that comes in their 

 way, however hurtful it may be. Schceffer says that he found great 

 difficulty in keeping the Branchipiu alive after having been taken out 

 of the water in which they were found, and also says that they are 

 incapable of bearing any degree of cold. Jurine, however, found no 

 difficulty in hatching the ova of the Chirocephalwi sent to him by 

 Prevost, and keeping the animals so hatched till they reached matu- 

 rity ; and Shaw distinctly asserts that he has found them in this 

 country, in shallow pools, in the months of December and January, 

 even after pretty sharp frosts, as lively almost as in spring or summer. 

 I have always found them in the months of October, November, and 

 December, and even after frosts of short continuance though of con- 

 siderable severity. In general they have been very short-lived after 

 being removed trom their native habitat, but I have been able to 

 hatch the young and watch their progress to maturity. Though 

 they do not appear destructive to other animals, they fall an easy prey 

 themselves to various enemies. Frogs, salamanders, the larvae of the 

 Dyteici, the Cypridet, and other such inhabitants of the water, kill them 

 in vast numbers ; and they seem besides, according to Prevost, to be 

 specially infested by a species of Vorticella, or wheel-animalcule, 

 which attaches itself to the body of the animal in great numbers, and 

 would very soon, were it not for their moulting frequently, completely 

 destroy it. I have found them very liable to a peculiar disease which 

 seems very frequently to terminate fatally. It attacks their body 

 near the external ovary, the lower part of the abdomen, &c., and the 

 branchial feet are not exempt from it It consists of a white growth, 

 composed of a fatty sort of substance, and when once this appears, 

 the poor animal almost always soon after dies." 



After impregnation "the ova appears at first as small white 

 spherical bodies lying in the internal ovary, which stretches along 

 the abdomen, and then passing from it into the external ovary 

 already described. When the proper time arrives the mother deposits 

 ova loose in the water, the ovary opening at the point, and 

 the eggs being thrown out by a sudden jerk to the number of 10 or 

 12 very rapidly. The whole process of laying lasts several hours, 

 sometimes, according to Prevost for a whole day, and the number of 

 ova excluded vary from 1 to 400. At first the egg is yellowish 

 spherical, beset all round with short setae, but when it has been for 

 a short time exposed to the action of the air and the witer, it 

 assumes an irregular hexagonal figure and a greenish hue. In about a 

 fortnight or so the egg is hatched and the young one issues forth, but 

 very unlike its parent. It consists of two nearly equal oval portions, 

 head and body." 



According to the recent observations of Dr. Zenker (' Physiological 

 Remarks on the Daphnidae," translated in vol i. of ' Microscopical 

 Journal') and others, it appears that the female Daplmidce have the 

 power of producing eggs which are fertile without access to the 

 male. This is what occurs in some of the Aphides for a given 

 number of generations. In the Dap/midce it appears to be without 

 limit. This reproduction from unimpregnated ova is quite analogous 

 to the process of gemmation amongst the lower animals. The 

 Efreat difference is that it takes place from the ovary and not from 

 some more general tissue of the body. In the Daphnidte, however, 

 ova are produced after impregnation, which differ from the other in 

 being enveloped in a fine corneous saddle-shaped shell which is called 

 an ' ephippium,' and such ova, as they are now known to occur in other 

 animals, are called ' ephippiau ova." Mr. Huxley however, who has 

 described them in Lacinularia socialis, a species of Rotifera, says they 

 " probably do not require fecundation, and are thence to be con- 

 sidered as a mode of asexual reproduction." 



In reference to this curious subject, Mr. Busk has added the 

 following note to Zenker's remarks ou Daphnidie, in the first volume 

 of the ' Microscopical Journal ': 



" The number of males is very considerable, and pretty nearly 

 equal to that of the females at all times of the year. This fact seems 

 to afford a curious confirmation to Dr. Zenker's opinion, that the 

 chief object of male impregnation is the production of ephippian, or 

 winter ova. In the case of Cliirocephalus this provision becomes 

 repeatedly necessary during the year, and not towards winter only ; 

 for it is a remarkable fact, on Blackheath at all events, that the 

 Chirocephalus is never found in any of the several ponds on the 

 heath, except in those which dry up completely, at least once, but 

 in some years several times, or for the whole summer continuously. 

 The ponds inhabited by the Chirocephalus, in fact, are merely pools 

 formed by the drainage from the roads. Now, it is manifest under 

 these circumstances that were not provision made by the formation 

 of winter ova, or ova having a thick double coat, for the revival of 

 the race after the drying up of their habitation, it would become 

 extinct. We accordingly find that such provision is made in the 

 numerous males at all times present. 



"The extraordinary power possessed by the ova of the Cliiro- 

 cephalua of resistance to the effects of desiccation is very remarkable, 

 as is also the readiness and rapidity with which they are developed 

 when again subjected to the influence of water. If the basin of a 

 small pool which has been dry and even dusty for mouths becomes 

 filled after a few days' rain, the water will be found swarming with 

 myriads of Chirocephall in about ten days or a fortnight ; or if a 

 piece of the dried bottom of such a pool be placed in a pailful of 

 water, numerous Ckirocephali will be hatched from it in the same 

 time. The reason for this curious arrangement with respect to the 

 Ckirocephali is obvious enough. These delicate creatures, themselves 

 vegetable feeders, are the prey of innumerable enemies ; among the 

 chief of which are the larva; of Dynticus, and of Dragon-Flies, &c. In 

 ponds which never dry up, these voracious enemies have time and 

 opportunity to destroy the whole race of Chirocephali ; but in the 

 favourite haunts of the latter, their enemies not being able to survive 

 the drying up of the water, are cleared off on each such occasion, and 

 the Chirvcephali being rapidly hatched, have, as a race, tune to 

 propagate and deposit their posterity in safety for another resur- 

 rection." 



Another point of interest with regard to Ckirocephalus is, that it 

 affords an instance of the nearest living type, to the extinct family 

 of Trilobitfs. [TRILOBITES.] Professor Burmeister, at the conclusion 

 of his laborious investigation into the structure and affinities of this 

 family, in his work on the ' Organisation of Trilobites' (translated 

 into English and published by the Ray Society), says, " The 

 Trilobitet were a peculiar family of Crustacea, nearly allied to the 

 existing Phyllopoda, approaching this latter family most nearly in 

 its genus Branchipus (Chirocephalut), and forming a link connecting 

 the Phyllopoda with the Pcecilopoda." 



CHIUO'NOMUS, a genus of Dipterous Insects of the family 

 Tipulidce. This genus was established by Meigwn, and is principally 

 distinguished by the following characters : Fourth joint of the 

 palpus longer than the rest; antennae 13-jointed, in the male, and 

 furnished with long hairs ; the antennae of the female are 6-joiuted, 

 and the hairs are short ; the anterior legs are inserted at some distance 

 from the others, and the anterior tarsi are generally very long ; the 

 wings when closed lie parallel, and they have three posterior cells ; 

 the body is long, slender, and hairy. 



Mr. Stephens, in his ' Catalogue of British Insects,' enumerates 

 upwards of eighty species of this genus : they are all of small size, 

 frequent marshy situations, and very much resemble gnats. The worm 

 known to anglers by the name of Blood- Worm is the larva of one of 

 the species of this genus the Chironamu plumosiu. This worm is 

 about half an inch in length ; the body consists of numerous segments, 

 and is furnished at the tail with several appendages which constitute 

 the breathing apparatus. It is seen during the summer months on 

 the mud near the edges of ponds and ditches ; when thus seen how- 

 ever it is only shifting from one place to another, its natural locality 

 being in the mud, where it may generally be found in great numbers, 

 living for the most part under water. This larva is much sought after 



