418 CRUSTACEA. 



its base a vesicular branchial appendage. The anterior, or even all 

 the legs (Leptodora) may have the form of prehensile feet, and 

 be destitute of branchial appendages. 



The Phyllopods possess a large pair of eyes, which are sometimes 

 fused together in the median line. In addition a small median 

 simple eye (Entomostracan eye) may persist. They have a saccular 

 or chambered heart, which controls the regular circulation. Coiled 

 excretory organs, known as shell glands, are sometimes present ; 

 they open to the exterior by a special aperture on the posterior 

 maxilla. The function of respiration is performed by the entire 

 surface of the body, the area of which is much increased by the 

 reduplicature of the skin forming the carapace ; also by the folia- 

 ceous swimming feet, and especially by the surface of the branchial 

 appendages. 



Reproduction. The Pliyllopoda are of separate sexes. The males 

 are distinguished from the females by the structure of the first 

 pair of antenna? which are larger and more richly provided with 

 olfactory hairs, and also by their anterior swimming feet which 

 are armed with prehensile hooks. In general the males are less fre- 

 quently met with than are the females, and, as a rule, only at definite 

 seasons of the year. The females of the smaller Pliyllopoda (Clado- 

 cerct) are able to produce eggs without copulation and fertilization ; 

 and these eggs, the so-called summer eggs, develop spontaneously and 

 produce generations containing no males. In certain genera of the 

 Branchiopoda, e.g., Artemia and Apus, parthenogenesis is the rule ; 

 the males, indeed, have only been known a few years. The females 

 usually carry the eggs about with them on special appendages, or in 

 a brood pouch beneath the shell on the dorsal surface. The just 

 hatched young either possess the form of the sexually mature animal 

 (Cladocera), or undergo a complicated metamorphosis, leaving the egg 

 membranes as a nauplius larva with three pairs of appendages (Bran- 

 chiopoda}. 



A few of the Pliyllopoda live in the sea, the greater number 

 inhabit stagnant freshwater ; some of them are found in brine pools. 



Sub-order 1. Branchiopoda.* Pliyllopoda^ with clearly seg- 

 mented body, often enclosed in a flat, shield-shaped, or laterally 

 compressed bivalved shell, with from ten to about thirty or more 

 pairs of foliaceous swimming feet. 



* Schiiffer. ' Der krebsartige Kieferfuss." etc. Regensburg. 1756. A. Kozu- 

 bowski, " Ueber den miiiiiiliclien Apus cancrifnrmis." Arclilc fur yatu-njcxi-Ji. 

 Tom XXIII. , 1857. C. Clans. " Zur Kenntniss des Baues und cler Eiitwickehniir 

 von Branckipus und Apus," etc., GSttingen, 1873. 



