THE FAIRY SHRIMPS (PHYLLOPODA) 



663 



small and often unsegmented. The second antennae are vestigial 

 or absent in the Notostraca; in the male anostracans they form 

 variously modified clasping organs; and in the Conchostraca they 

 are biramous swimming appendages. Male Anostraca often bear 

 frontal organs which may arise from the bases of the second anten- 

 nae or from the front of the head. The trunk-Hmbs are leaf-hke 

 in form (hence the name Phyllopoda) and are remarkable for hav- 

 ing gnathobases, or "chewing bases, " far removed from the mouth. 

 The first or the first and second pair are modified in male Con- 

 chostraca for clasping the female. In female Notostraca the limbs 

 of the eleventh trunk somite are 

 modified to form brood-pouches, or 

 "oostegopods," for carrjdng eggs. The 

 females of some Conchostraca have 

 the flabella of two or three limbs near 

 the genital aperture enlarged and the 

 egg masses are attached to these. In 

 the Anostraca the appendages of the 

 somites on either side of the genital 

 opening are modified for reproduction 

 in both sexes. 



In addition to the various appendages 

 which serve as accessory reproductive 

 organs, the oviducts unite to form an 

 external uterine chamber in the Anos- 

 traca, and the males of the same suborder have a copulatory organ 

 formed by the fusion of the extremities of the vasa deferentia. 

 All phyllopods are of separate sexes. Males are much less common 

 than females, in fact some species are known only from female 

 specimens, and the development of several is believed to be usu- 

 ally parthenogenetic. The gonads are paired and have a simple 

 tubular structure, except in the Notostraca where they are much 

 ramified. In the Anostraca the eggs are carried in the female's 

 brood-pouch, the uterine portion of the oviduct, sometimes until 

 they hatch. The Notostraca bear the eggs in the special receptacles 

 formed by the eleventh pair of trunk-limbs, and the Conchostraca 

 carry them enclosed in the valves of the shell. 



Fig. 



t, telson 

 X3. 



Apus aequalis. c, carapace; 

 d, cercopods or furcal rami. 

 (After Packard.) 



