20 



CRUSTACEA — BRANCHIOPODA 



side being nearly flat, the dorsal surface convex ; the hinder 

 margin of the head is indicated dorsally l>y a transverse cervical 

 ridge, bounded by two grooves, behind which the carapace projects 

 backwards as a great shield, covering at least half the body, but 

 attached only to the back of the head. In Lepidurus procluctus 

 the head and carapace together form an oval expansion, 

 deeply emarginate at the hinder, narrower end, the sides of 

 the emargination being toothed. The carapace has a strong 

 median keel. The kidneys project into the space between the 

 folds of skin which form the carapace, and their coils can be 

 seen on each side, the terminal part of each kidney-tube enter- 

 ing the head to open at the base of the second maxilla. In all 



Fig. 2. — Chirocephalus diaphanus, female, x 5, Sussex. D. 0, Dorsal organ ; //, heart ; 

 Oi\ ovary ; JJ, uterus ; T^, external generative opening. 



Branohiopoda with a well-developed carapace the kidney is enclosed 

 in it in this way, whence the older anatomists speak of it as the 

 " shell-gland." 



Associated with the development of the carapace, in this and 

 in the next family, is a remarkable condition of the lateral eyes, 

 which are sessile on the dorsal surface of the head, and near the 

 middle line, the median eye being slightly in front of them. 

 During embryonic life a fold of skin grows over all three eyes, so 

 that a chamber is formed over them, which communicates with 

 the exterior by a small pore in front. 



In the LiMNADiiDAE the body is laterally compressed, and 

 the carapace is so large that at least the post-cephalic part 

 of the body, and generally the head also, can be enclosed 

 within it. 



In Zimnetis (Fig. 3) the dorsal surface of the head is bent 

 downwards and is much compressed, the carapace being attached 



