334 Introduction to Animal Morphology. 



moscs of its ducts. This and the preceding gland 

 may be homologous, and possibly the " roots" of Rhi- 

 zocephala may represent its ducts. 



Beside the intestine in the abdomen is a mass of 

 connective tissue and undifferentiated protoplasm, 

 containing yellowish or reddish fat : these are largest 

 proportionally in Entomostraca, and are among the 

 chief sources of the oil which many fishes store in 

 their livers. In Copepods this adipose body has a la- 

 cunary structure, and may act as a mesentery. Di- 

 gestive organs are absent in the rudimental males of 

 Cirripedes and parasitic Copepoda. The intestine is 

 absent in Monstrilla. 



The body cavity contains blood, which is colorless, 

 reddish, or pale violet, with nucleated white corpus- 

 cles. A heart exists (except in Cyclopidae, Corycsei- 

 dae, Harpactid.r, and IVltididse, among Copepoda, 

 most Ostracodes, and a few others) as a dorsal vessel, 

 whose simplest form, as in Cladocera, is a sac, over 

 the intestine, receiving blood by two lateral openings 

 ^cuoits ostiii : , and sending it forward by one short 

 stem to bathe the brain, and enter the interstices of 

 the tissues, from whence it is returned to the heart. 



In Pontellidse and Calanidae there is a posterior ostium as 

 well as t\vo lateral ; and in Calanclla the aorta is longer, and 

 divides into two. In Argulus there is one ventral osculum, 

 and the blood is sent by the heart partly through the body 

 and partly through amedio-posterior opening to the gill-like 

 appendages. In Phyllopoda the heart is elongated, and com- 

 posed of successive chambers (twelve in Apus), like a chain 

 of communicating Daphnia hearts. These have many ostia 

 (twenty pair in Artemia), but they do not correspond to the 

 metameres, as there is usually one for several somites. In 

 Poecilopoda the heart is surrounded by a pericardiac sinus ; 



