294 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



As can be seen in figure 15, the stomach wall is made up of an outer 

 muscular coat composed of fine muscle fibers arranged in a thin con- 

 nective tissue. This is lined by an endothelium of large nucleated 

 cells, which covers the entire inner surface of the stomach and extends 

 into all the lobes. 



There is no differentiation of the anterior third of the stomach by a 

 thin chitinous cuticle, thrown up into longitudinal folds, and cor- 

 responding to the chitinized gizzard found in other Crustacea. The 

 only noticeable difi'erence is that the cells toward the posterior end 

 of the stomach are larger and more columnar, while those at the 

 anterior end are smaller and more of a pavement epithelium. 



Scattered about among the columnar cells at the posterior end are 

 a limited number of much larger vacuolated cells which project into 

 the stomach cavity (gc). Their free ends are rounded and filled 

 with large spherical or ellipsoidal masses which stain deeply with 

 eosin. This suggests that they probably correspond with the 

 so-called fat globules found by Hartog in the cells of the posterior 

 portion of the stomach of Cyclops. 



THE NERVOUS SYSTEM AND SENSE ORGANS. 



General structure. — The nervous system is made up, as usual, of 

 two ganglia connected by a commissure around the esophagus, and 

 a ventral cord which reaches to about the center of the genital seg- 

 ment. But the structure and arrangement of these different parts 

 presents many striking peculiarities (fig. 15). In the first pla^e, the 

 backward migration of the mouth and esophagus has carried the 

 two ganglia and the connecting commissure along the ventral sur- 

 face to the extreme posterior margin of the cephalon. This, coupled 

 with the fact that the eye is in actual contact with the ventral sur- 

 face, has removed every portion of the nervous system from the 

 dorsal part of the body. Ganglia, nerve cord, commissures, and 

 sense organs are as completely ventral as they are dorsal in any 

 vertebrate. The ordinary terms supra and infra are hence rather 

 out of place when applied to the respective ganglia; pree and post 

 become far more appropriate. 



Furthermore, as a result of this backward migration, or from 

 other causes, each of the ganglia is enormously elongated, so that 

 together they extend practically the entire length of the cephalo- 

 thorax. They thus become more markedly the ventral counterpart 

 of the dorsal nerve cord in vertebrates. 



Prseesoj)hageal ganglion. — This is a long and club-shaped mass, 

 extending from the esophagus to the anterior end of the stomach. 

 It is strongly flattened dorso-ventrally, of about the same width for 

 the posterior two-thirds of its length, then tapers rapidly into the 

 comparatively long optic nerves, which lie side by side and partially 



