ENTOMOSTRACA. 



[ 287 ] 



ENTOMOSTRACA. 



testiiial canal is usually straiplit or but 

 slightly curved ; sonietiiues, however, it is 

 coiled (fig. 7). The Entomostraca are 

 mostly herbivorous, although some are car- 

 nivorous. The sexes have not been distin- 

 guished in all the Eutomostraca, although in 

 some they are perfectly distinct. It appears 

 also that in certain of them, reproduction 

 takes place according to the law of alterna- 

 tion of generations — females only being 

 produced through several generations, and 

 the males appearing only at certain seasons. 



The spermatozoa are often of most re- 

 markable structure (see Spermatozoa). 

 The ova are mostly rounded ; sometimes 

 tbev are covered with spines, and often 

 brilliantly coloured. They are either 

 hatched in the external ovaries mentioned 

 above, or in a space between the body of 

 the parent and the posterior part of the 

 shell ; or they are deposited in massi>s upon 

 and glued to water-plants, and hatched in- 

 dependently of the parents. 



At particular seasons of the year, the ova 

 in certain species are furnished with thick 

 capsules, and imbedded in a dark opaque 

 substance presenting a minutely cellidar 

 appearance, and occupying the above-men- 

 tioned interspace between the body of the 

 animal and the back of the shell (fig. 37 a). 

 This is called the ephippium, and the ova 

 ephippial or winter ova (Eggs). 



"\\ hen first hatched, the young (fig. 16) 

 difier very strikingly in form and structure 

 from the adults (figs'. 8, 9). 



The larval forms of the higher Crustacea 

 often bear considerable resemblance to the 

 perfect Entomostraca. 



The minute structure of the Entomostraca 

 is difficult to determine ; for although the 

 bodv and shell are frequently comparatively 

 transparent, the parts are exceedingly deli- 

 cate and soft, so that they are easily crushed 

 and mutilated,and their appearance distorted. 



The Entomostraca are best preserved in 

 solution of chloride of calcium or glycerine 

 (see Preservation). Some use glyceriue- 



jelly. 



A large number of Entomostraca are 

 found fossil ; among which must be specially 

 mentioned the Trilobites, of which 1600 

 species are described. 



The following systematic arrangement 

 comprises the most common genera and 

 species. Numerous others are described, 

 Brady enumerating 67 genera of the Cope- 

 poda'ouly: these are briefly mentioned mi- 

 der the individual heads. 



lyegion 1. Lophyropoda. Branchi.ie at- 

 tached to the organs of the mouth ; leg8 

 few, not exceeding five pairs, serving for 

 locomotion, articulation mostly more or 

 less cylindrical ; anteunie two pairs, one 

 pair used as organs of motion. 



Order 1. Ostracoda. Shell consisting of 

 2 valves, entirely enclosing the body ; 

 feet 1-3 pairs, adapted for progression ; 

 no external ovary. 



Sect. 1. PoDocoPA. Inferior antennae sim- 

 ple, subpediform, geniculate, clawed 

 at the end. (Includes all the fresh- 

 water and most of the marine Ostra- 

 coda.) 



Fam, 1. Cyprid^. Superior antennoe 

 mostly 7-jointed, with a dense brush 

 of long setae ; eye usually single ; feet 

 2 pairs, the last bent up between the 

 valves ; abdominal rami 2, elongate, 

 clawed at end. 

 Gen. : Cypris (PL 20. figs. 5 & 19), Can- 

 dona^ Cypridopsis, Pai-acypris, Ac/Iaia, 

 Notodromas, Fonto(ypris, Argiiloecia, 

 Bairdia, Macrocypris, and Chlamydo- 

 theca. 



Earn. 2. Cytherid^. Superior antennae 

 5-7 -jointed, setigerous or spinous; in- 

 ferior 4-6-jointed, without a brush; 

 feet 3 pairs, ambulatory ; post-abdo- 

 men rudimeutaiy, consisting of 2 very 

 small lobes. (Comprises most of the 

 marine species, and almost all the nu- 

 merous fossil species.) 

 Gen. : Cyfhere (PI. 20. tig. 2Q), Limnon/- 

 there, Cytheridea., Eucythere, Ilyobates, 

 Liixoconcha, Xestoleheris, Cytheriira, 

 Cytlieropteron^ Bythocy there, Cythe- 

 rideis, Sderochilus, and Paradoxo- 

 stoma. 



Sect. 2. Myodocopa. Inferior antennae 

 2-branched : one branch rudimentary, 

 the other powerful, many-jointed, with 

 long natatory setae ; mandibular palp 

 very large, subpediform, geniculate, not 

 branchial. Post-abdomen with 2 broad 

 plates, clawed. 



Earn. 3. Cytrldinidje. Feet 1 pair; ver- 

 miform, annulated, long; mandibles 

 obsolete ; second pair of jaws with a 

 large branchial plate ; eyes, 2 com- 

 pound, 1 simple. 

 Gen. : Cypn'dhin, Asferope, Btadyn'nefus 

 {Eurypjyius), Fhilomedes, Cylindrole- 



