220 Journal of Comparative Neurology, 



usually been considered nervous.^ Ectodermic ingrowths 

 occur here, the fate of which w^e shall consider later. A pair 

 of ingrowths, one on either side, penetrates the dorsal muscle 

 band, detaching a portion (imi. d^.) equal perhaps to one- 

 half the lateral band, in width. These ingrowths grow dorsally, 

 overarch the digestive tract and bloodvessel, and unite in a me- 

 dian position, producing the supra-oesophageal ganglia or brain. 

 A similar pair of ingrowths penetrates the ventral muscle band 

 near its margin and contributes directly to the growth of the 

 ventral cord and to the formation of the sub-oesophageal gan- 

 glia. The connective {cont. ar'ce.), as its fibers grow from the 

 brain toward the ventral cord, passes superficially to the detached 

 portion of the dorsal muscle band, re-enters the body cavity at 

 the break between the dorsal and lateral bands, — the place of 

 occurrence of the lateral line cells, — passes superficially to the 

 detached portions of the ventral muscle {imi. v^.), and joins the 

 ventral cord by way of the ectodermic ingrowths penetrating 

 that band. (Fig. 2.) The circum-oesophageal connective thus 

 comes to embrace, within its circuit, four strands of musle fibers. 

 These persist in this position and bec'ome functional in the pos- 

 terior zooid. 



It seems further probable, from my studies, that there is a 

 multiplication of nervous cells in the horns of the cord itself, which 

 are responsible for at least a portion of its increased prominence. 



In the preanal, segment-forming zone of the anterior zooid, 

 where the ventral cord is being extended caudad, there is a me- 

 dian constituent contributed by the ectoderm, in addition to the 

 two latero-ventral contributions mentioned for the posterior in- 

 dividual. The cord readily shows the extent of the single me- 

 dian and paired lateral components, in the newer segments. 



* Since the above investigations were made Brode's excellent paper on the 

 finer anatomy of Dero vaga has appeared. This author is convinced that the 

 lateral line cells are not nervous in character. While my own investigations 

 have caused me to hesitate in accepting the common view concerning them, I 

 am not in a position to corroborate or controvert Brode's conclusions. 



