561 



ENTOMOSTRACA. 



ENTOMOSTRACA. 



502 



had never seen a Lerntea change its skin. The antennas of the 

 Entomoitraca, the form and number of which vary much, serve in 

 many for swimming. The eyes are very rarely placed upon a pedicle, 

 and when they are so placed the pedicle is no more than a lateral 

 prolongation of the head, and is never articulated at its base. The 

 last-named organs are often very much approximated, and even 

 compose one only. The tail is never terminated by a fan-shaped fin, 

 and never presents the false feet of the Malacostraca. The eggs are 

 collected under the back, or external, and under a common envelope, 

 having the form of one or two small groups situated at the base of the 

 tail. They possess the power of preserving their vitality for a long 

 time in a state of desiccation. [BiNocULUs.] It would appear that 

 not less than three moults are undergone by many of these animals 

 before they become adult and capable of propagating their species, 

 nd it has been proved, in the case of some of them, that a single 

 copulation will fecundate many successive generations. [BRASCHIOPODA.] 

 Dr. Buird, in his interesting Monograph on the British Entomoitraca, 

 gives the following general account of this family : 



" The greater number of these little creatures are furnished with 

 branchix, either to their feet or maxillae, and when noticed in their 

 native habitats, may be seen to have them constantly in motion, their 

 action being seldom interrupted. One chief use therefore of them in 

 the economy of nature may be, as Miiller says, to ventilate the water 

 day and night ; and as they chiefly reside in standing pools, they may 

 thus be of great use in preventing them from becoming soon putrid. 



" As this may be considered,one of the benefits conferred by these 

 insects, it may be useful to know the evils to man they may be likely 

 to produce. 



" Though they are most abundant in stagnant water, they yet occur 

 in considerable numbers in the purer sorts of water that serve as our 

 common drink, and may frequently be seen even in the drinking 

 water of London, Edinburgh, and other large towns; and Miiller 

 asserts very gravely, that as we thus drink them alive, and with their 

 eggs, he would not be surprised were we to discover them some day 

 in the human intestines. ' The time,' he says, ' is at hand, when 

 the causes of disease shall not only be sought after in the air, in our 

 method of living, &c., but in the incautious use of waters often 

 abounding in innumerable animalcules." According to Miiller and 

 Straus, the greater number of the Entomottraca, not parasitical, live 

 upon vegetable matter, and not upon animals ; and the former, in an 

 experiment he instituted, says, that in keeping a number of species, 

 such as the Daphnia pcnnata and longiipina, Cyprit itrigala and 

 pilota, Lynceut iphtricuf, and Cyclops i/uadricornii, in the same water 

 from the 24th of July to the 22nd of January, during which time the 

 water had evaporated from a depth of five inches to that of one, he 

 frequently subjected small quantities of this water to the microscope, 

 and he was never able to discover any animalcules in it upon the 

 most attentive examination, though the intestines of the Entomostraca 

 themselves were seen to be full, sufficiently proving that 'they had 

 not fasted during that time. This assertion however I am much 

 inclined to call in question. The Cyprides particularly seem to be 

 most voraciously carnivorous ; and I have invariably found it exceed- 

 ingly difficult to keep for a length of time any other Entomostraca 

 alive in the same vessel with the larger species of Cyprit. In a vessel, 

 in which I have kept full grown Chirocephali, there were mixed with 

 them many specimens of the Cyprit triitriata. In a few days the 

 .'tphali might be seen to become languid in their movements, 

 and assume an unhealthy appearance. The Cyprulet had become 

 their deadly enemy. They might be seen ever and anon to fasten 

 themselves to the delicate feet of the poor Chirocephali, and 

 wofully impede their course through the water ; and when, either 

 from these annoyances, or from any other cause, they ceased to be able 

 to move with any degree of rapidity, hosts of these little Carnii'ora 

 might be observed to attack them before life was extinct, anticipating 

 as it were their victims' death. Then, when life had fairly ceased, 

 they rioted upon their flesh, and in a few hours little but the external 

 covering was left. 



" I have no doubt that most of the Entomoitraca are essentially car- 

 nivorous, and I have frequently seen specimens of Cyprit in their 

 turn, as soon as dead, attacked immediately by quantities of the 

 Cyclopi quadricornis, who in a few minutes had fastened themselves 

 upon the dead animal, and were so intent upon their prey that they 

 were scarcely frightened away from it by being touched with a brush. 

 Im a short time the Cypris might be seen lying at the bottom of the 

 vessel, the valves of the shell separated and emptied of their contents. 

 Leuwenhoek and De Oeer not only maintain that the Cyclops nuad- 

 ricomis lives upon animalcules, but that it even preys upon its own 

 young, a fact which I have also noticed myself. Jurine asserts that 

 the Cyclopi quadricornis is carnivorous from taste, and only herbi- 

 vorous from necessity ; while the Daphnia pulex, he distinctly affirms, 

 lives upon animalcules. Place a few Entomoitraca, such, for example, 

 a the Daphniir, Chirocephali, Lyncei, &c., in a vessel with clear pure 

 water, and only some vegetable matters in it, and they gradually 

 become languid, transparent, and finally die ; but mix with this 

 water some which contains numerous fnftuoria, and the Entomostraca 

 will then be seen speedily to assume another aspect. They become 

 lively and active, and the opacity of their alimentary canal testifies 

 sufficiently the cause of it. When indeed we consider the amazing 

 HAT. HIBT. DIV. VOL. II. 



quantity of animals which swarm in our ponds and ditches, and the 

 deterioration of the surrounding atmosphere which might ensue from 

 the putrefaction of their dead bodies, we see a decided fitness in these 

 Entomostraca being carnivorous, thus helping to prevent the noxious 

 effects of putrid air which might otherwise ensue ; whilst they in 

 their turn become a prey to other animals, which no doubt serve 

 their purposes also in the economy of nature. 



"The fresh-water Gammari seem to prey upon them, and the 

 ffydrachnce are their decided enemies; 'for,' says Miiller, 'they seize 

 hold of them while swimming by their feet, and daintily suck the life's 

 blood out of their captives with their sharp beaks. The Hydra also, 

 and not a few aquatic larvee, lay snares for them ; and many Vorticdlce 

 frequently greviously infest them, for they not only adhere (often in 

 heaps) to the members projecting beyond the shell, but they overspread 

 the whole body with their own colonies, not a little retarding the 

 motion and agility of their host.' The larva of the Corethra plumi- 

 cornis, known to microscopical observers as the Skeleton Larva, 

 is exceedingly rapacious, more especially of the Sap/mice. They seize 

 their prey with the rapacity of a pike, grasping it with their two strong 

 jaws and gorging it alive. Pritchard says they are the choice food 

 of a species of Naia, which he calls the Lurco, and which devours 

 them in great numbers. The Chydorus sphericus is their especial 

 favourite, and I have repeatedly verified Pritchard's observations, 

 having counted at least ten individuals swallowed alive, and lodged in 

 the different stomachs of this glutton. Those in the first and second 

 stomachs were still alive, while those contained in the inferior ones 

 were more or less partially decomposed. 



" The marine species are also preyed upon by their different 

 enemies, amongst which are the Heroes. ' The fact of Heroes feeding 

 upon small Crustacea,' says Mr. Paterson, ' has been recorded by 

 Fabricius, and at present appears to rest upon his authority. It was 

 interesting to observe the fact, which I did, without knowing it was 

 previously known. The Crustacea were almost as visible in the 

 transparent body of the Seroe as they had previously been, and very 

 conspicuous by the bright green of their colouring.' 



" That the Entomostraca form a considerable portion of the food of 

 fishes hag been long observed, and it is very probable that the quality 

 of some of our fresh-water fishes may in some degree depend upon 

 the abundance of this portion of their food. Dr. Parnell informs us 

 that the Loch Leven trout owes its superior sweetness and richness of 

 taste to its food, which consists of small shells and Entomottraca. The 

 colour of the Loch Leven trout, he farther informs me, is redder than the 

 common trout of other localities. When specimens of this fish have 

 been removed from the Loch and conveyed to lakes in other places, 

 the colour remains, but they very soon lose that pecxiliar delicacy of 

 flavour which distinguishes so remarkably the trout of Loch Leven. 

 The experiment has been repeatedly tried, and always with the same 

 results. The Bansticle devours them with great rapidity ; and I have 

 seen two or three individuals clear in a single night a large basin 

 swarming with Daphnice, Cyclops, &c." 



The following is the arrangement of this family adopted by Dr. 

 Baird : 



Sub-Kingdom ANNULOSA. 

 Class CRUSTACEA. Division ENTOMOSTRACA. 



Legion I. BHANCHIOPODA. [BRANCHIOPODA.] 

 Order I. PHILLOPODA. 



Family 



1, APODID.E, containing 1 , 



one genus ..... J * 

 Family 2, NEBALIAM;, containing I , ,. 



one genus ..... J 

 Family 3, BRANCHIPODIDJS, con- 1 Chirocephalus. [CHIHOCEPHALUS.] 



taining two genera . . . J A rtemia. [ARTEMIA.] 



Order II. CLADOCERA. 

 Daphnia. 

 Moina. 

 Sosmina. 

 Macrolhrij;. 

 Sida. 



Daphnella. 

 Family 2, POLYPBEMID.E, contain- f Polyphemus. 



Family 1, DAPHNIAD,E, containing 

 six genera ..... 



[DAPHNIA.] 



ing two genera 



Family 3, LvscEin.fi, containing 

 seven genera . 



Evadne. 



Euryccrcus. 



Chydorus. [CHYDOHUS.] 



Camptocercut. 



A croperus, 



Alona. 



Pleuroxui. 



Peracantha. 



Legion II. LOPHYROPODA. 

 Order I. OSTHACODA. 



Family 1, CYPRIDID/E, containing 

 five genera . . . 



r Cypris. 

 I Candona. . 

 { Cylhere. [( 



Cylhere. [CYTHERE.] 



Cythereis. 



Cypridina. 



