ENTOMOSTRACA. 



[ 231 ] 



ENTOMOSTRACA. 



^vinter-ova; and the envelopes are supposed 

 to act as a defence from the. cold of winter 

 (Eggs). 



When first hatched, the young (fig. 16) 

 difi'er ver}^ strikingly in form and structm-e 

 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 very difficult to determine ; for although 

 the body and shell are frequently compara- 

 tively transparent, the parts are exceedingly 

 delicate 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 (see Preser- 

 vation). 



Some of the Entomostraca are found fossil. 



Systematic arrangement. 



Legion 1. Lopliyropoda. Branchiae at- 

 tached to the organs of the mouth; legs 

 few, not exceeding five pairs, serving for 

 locomotion, articulations mostly more or less 

 cylindrical -, antennae two pairs, one pair 

 used as organs of motion. 



Order 1. Ostracoda. Shell consisting of two 

 valves, entirely enclosing the body ; legs 

 two or three pairs, adapted for progres- 

 sion ; no external ovary. 



Fam. 1. CvPRiDiE. Superior antennae long, 



with numerous joints, and a pencil or 



tuft of long filaments ; inferior stout 



and pediform; eye single; legs two pau's. 



Candona, Cypris. 



Fam. 2. Cytherid^. Superior antennae 

 without the pencil of long filaments ; 

 eye single ; legs three pairs. 

 Cythere, Cythereis. 



Fam. 3. CvpRiDiNADiE. Both pairs of 

 antennae pediform ; eyes two, peduncu- 

 lated; legs two pairs, one pair always 

 enclosed within the shell, and of remark- 

 able structure ; abdomen terminated by 

 abroad lamellar plate, with strong hooks 

 and spines. 

 Cypridina. 



Order 2. Copepoda. Shell jointed, forming 

 a buckler, enclosing the head and thorax ; 

 legs five pairs, mostly adapted for swim- 

 ming; ovary external. 



Fam. 1. CvcLOPiDiE. Head consolidated 

 with the thorax; foot-jaws two pairs, 

 generally small; legs five pairs, the 



fifth pair rudimentary ; eye single ; both 

 superior (larger) antennae in the male 

 fiu'nished with a swollen hinge-joint. 



Cyclops, Canthocamptus, Arpacticus, 

 Alteutha. 



Fam. 2. DiAPTOMiDiE. Head consolidated 

 with the first joint of thorax ; foot-jaws 

 three pairs, well developed; legs five 

 pairs, the last pair differing in structure 

 fi'om the others, and differing from each 

 other in the two sexes ; eye single, 

 sometimes pedunculated in the male; 

 right antenna only Avith the swollen 

 hinge-joint in the male. 



JDiaptomus, Anomalocera, Temora. 



Fam. 3. CETOCHiLiDiE. Head consolidated 

 with first joint of thorax; foot-jaws 

 three pairs, strongly developed; legs 

 five pairs ; eyes two ; right antenna 

 only with the hinge-joint in the male. 

 Cetochilus. 

 Provisionally NotodelpTiys. 



Legion 2. BrancMopoda. Branchiae at- 

 tached to the legs ; legs from foiu" to sixty 

 pairs. 



Order 1. Phyllopoda. Legs fi'om eleven to 

 sixty pairs in number, joints foliaceous 

 and branchiform, chiefly adapted for re- 

 spiration and not motion ; eyes two or 

 three, sometimes pedunculated ; antennae 

 one or two pairs, neither adapted for 

 swimming. 



Fam. 1. Branchipodida. Body not en- 

 closed in a carapace or shell ; antennae 

 two pairs, the inferior with prehensile 

 appendages in the male; legs eleven 

 pairs. 



Artemia, Branchipus. 



Fam. 2. Aspidephora. Body enclosed in 

 a shell ; antennae one or two pairs ; 

 legs more than eleven pairs. 

 Apus, Nebalia. 



Order 2. Cladocera. Legs four to six pairs, 

 chiefly branchial ; eye single and very 

 large; antennae two pairs, inferior large, 

 branched and adapted for swimming. 



Fam. 1. Daphniad^. Superior antennae 

 very small, inferior large, two-branched; 

 legs five or six pairs, all enclosed within 

 the carapace ; eye single, large. 



Daphnia, Daphnella, Macrothrix, 

 Moina, Bosmina, Sida. 



Fam. 2. Polyphemid^. Inferior antennae 

 two branched, one branch four-, the 

 other three-jointed ; lower part of shell 

 forming a large vacant space for con- 



