STROPHOMENIA OPIIIDIANA. 115 



usual in the genus unites with its fellow of the opposite side so close to the cloaca 

 that two openings appear to be present. The cells are all of columnar form and 

 are of one type judging from the darkly staining granular secretion. As in other 

 species of the genus a diverticulum of the cloacal wall is present ventral to the 

 outlet of the shell gland, but there are no indications that it is of any especial 

 significance. 



In the other species of the genus Strophomenia described in the present 

 paper there are from few to many diverticula extending outwardly from the 

 cloacal wall, but they never reach the excessive development existing in this 

 species. These are shown, somewhat diagrammatically (Plate 9, fig. 1). The 

 cells are usually columnar and are filled with a finely granular sul)stance which in 

 various places is in the act of escaping into the cloacal cavity. 



The brain, clearly bilobed, is located against the under side of the intestinal 

 coecum at the level of the posterior border of the atrium (Plate 8, fig. 5). From 

 it the usual three pairs of nerves originate, that after branching unite with 

 ganglionic masses attached to the bases of the cirri or without such union pass 

 to the body wall. The connectives to the lateral, pedal, and labio-buccal sys- 

 tems arise in the customary situations and the relations of the ganglia themselves, 

 so far as they have been determined, are typical. Pedal commissures and 

 latero-pedal connectives occur at frequent, though not perfectly regular, inter- 

 vals and a corresponding number of unusually heavy nerves arise from the dorsal 

 surface of the lateral ganglia. These have in several cases been followed close 

 to the mid dorsal line but that they form commissures is not assured. They 

 probably innervate the neighboring somatic musculature and hypodermis. 



Posteriorly the pedal cords, united by commissures to the anterior cloacal 

 wall, branch repeatedly in this last named locality and innervate the body and 

 cloacal walls and some of the fibres become imbedded in the shell gland. The 

 lateral cords at this same level likewise branch repeatedly and supply the same 

 structures as the pedal, though more dorsally, and in addition give off a few 

 small nerves that attach themselves to the pericardial wall. A very few 

 branches from these last named nerves have been traced a short distance into 

 the heart. The pedal and lateral cords are posteriorly united by one delicate 

 branch; others may exist, but the nerves are not sufficiently differentiated from 

 the surrounding tissue to permit of their being followed for any considerable 

 distance. It is a peculiar fact that no trace of a dorsal posterior commissure 

 uniting the lateral cords has been found to exist. 



The labio-buccal connectives arise to the inside of the connectives leading 



