KLEINENBERG ON DEVELOPMENT OP LOPADORHYNCHUS. 541 



in the body cavity, and settle anywhere on its walls. In the 

 male, masses of cells are shed off into the body cavity, which 

 become spermatoblasts. 



There remains to be described the development of the pharynx 

 and oesophageal glands of the adult. The stomodseum of the 

 larva does not become the pharynx, but the latter is derived 

 from a pair of gland-like stomodseal outgrowths, which subse- 

 quently fuse together and form the pharynx. The oesophageal 

 glands are formed as three outgrowths — two lateral, one median 

 and dorsal, from the pharynx. 



The important facts which are to be gathered from the 

 foregoing account are these : Lopadorhynchus has no meso- 

 blast in the sense of a germ layer composed of undifferentiated 

 cells. The larva has its own nervous system and its own 

 musculature, no parts of either of which pass over to the adult, 

 but are replaced by a new nervous system and musculature, 

 and are afterwards aborted. The central nervous system of 

 the adult is formed from a number of separate centres or foun- 

 dations, the situation of which is in part determined by the 

 pre-existing nerve centres of the larva, although the latter 

 have no direct share in their formation, but act only as foci, 

 in connection with which fresh groups of nervous elements are 

 differentiated. 



The muscular system of the adult is derived wholly from the 

 ventral plates, as is also the whole ventral chain of ganglia, 

 with its connectives and commissures. These ventral plates 

 are, in their earlier stages, nothing more than thickenings of 

 the ordinary ectoderm, the cells of which become subsequently 

 divided into muscle-plates and neural plates. The muscle- 

 plates give rise to the whole of the muscular system, both of 

 the body walls, and of the gut ; but they do not split into two 

 layers, comparable to somatopleure and splanchnopleure, the 

 coelom being formed simply as an extension of the space exist- 

 ing between ectoderm and endoderm, the peritoneal walls of 

 which are formed by cells derived from the muscle- plates. 

 The neural plates give rise to the whole of the ventral ganglion 

 chain, and besides this to other and different organs, viz. the 



