Ou CephalogonimiTs vesicaudus n. sp. 253 



the openings of the last pair of lateral branches iuto the main stem 

 of the excretory vesicle and the connection of this with the caudal 

 vesicle. Fig. 4 is from an adjacent section which passes obliauely 

 thru the caudal vesicle and its pore to the exterior and just above 

 the opening from excretorj^ into caudal vesicle. Fig. 5 represents 

 part of a section which cuts this vesicle transversely. It may be 

 Seen from these four flgures that the caudal vesicle has a general 

 form whicli is approximately spherical or spheroidal but whicli is 

 modified by the presence of a number of longitudinal infoldings of 

 its wall (Fig. 6) which subdivide its cavity into a corresponding 

 number of pockets. These open laterally from the central cavity 

 wiüch is continuous from the mouth of the main excretory trunk to 

 the excretory pore or caudal foramen. The longitudinal infoldings 

 of the wall may be compared to the septae of an actinian and the 

 cavity of the caudal vesicle has therefore a shape not dissimilar to 

 that portion of the gastrovascular cavity of the actinian below the 

 gullet. The infolded wall consists of a thin structureless membrane 

 continuous at the edges of the excretory pore with the outer covering 

 of the body and at the junction of the excretory trunk with the 

 vesicle, continuous with tlie basement membrane beneath the epi- 

 thelial lining of the excretory vesicle. Within the caudal vesicle, 

 lining its w^all and covering all of the infoldings, is a layer of 

 finely granulär material of indifferent staining power. Its thickness 

 is fairly uniform and about equal to that of the epithelial lining of 

 the larger excretory ti'unks, but no nuclei, cell boundaries nor other 

 definite evidence of cellular structure can be made out. The tran- 

 sition from the condition of the lining of the excretory trunk to 

 that of the vesicle is sharp. In regard to the actual cliaraeter of 

 the lining of the vesicle I have not succeeded in obtaining any 

 conclusive evidence. It has the same character in the youngest 

 specimen that I have studied as in older and larger ones. 



Around the wall of the vesicle is a layer of large pyriform 

 cells represented in Fig. 7. They have prominent nuclei containing 

 four or live rather large clumps of chromatin. The cytoplasm is 

 clear non granulär. It is possible that these are glandulär in func- 

 tion and that the granulär appearing material lining the caudal 

 vesicle is a product of the activity of these cells. Corresponding 

 cells are not present about the wall of the excretory vesicle but 

 similar smaller cells are present in the subcuticular layer in many 

 legions. Embedded in the otherwise structureless wall of the 



Zool. Jahrb. XXXIII, Abt. f. Syst. 18 



