186 The Development of the Eye Muscles in Aeanthias 



thickened walls. He homologised this with the anterior prolongation 

 of the first somite observed by him in Pristiurus and Scyllium. He 

 therefore considered it as merely a secondary subdivision of that cavity. 

 Miss Piatt, 91, observed similar cavities in Aeanthias, and to her is 

 due the name of " anterior head cavities " ; it seeming unwise to alter 

 the numbering of the remaining head somites for the sake of a pair 

 of somites which are only known to occur in two forms. It also de- 



A. V. 



OS. V. 



S. A. 



Op. Ves. 



Fig. 1. — Reconstruction of auditory and optic vesicles, ganglia of fifth and 

 seventh nerves and the anterior, first, second and third somites of the right side of 

 an Aeanthias embryo, 12}^ mm. total length. Lateral view. 



serves mention that Zimmermann, 91, p. llo, recognized, in the same 

 year and quite independently of Miss Piatt, the presence in Aeanthias, 

 of this somite. According to Miss Piatt, the archenteron, which ex- 

 tended forward to the anterior neuropore as a solid mass of cells, was 

 divided into an anterior and a posterior part by the down-growing 

 infundibnlum. Both parts .grew laterally; the anterior forming the 

 anterior head somite, the posterior the 1st or premandibular somite. 

 Hoffmann was able to add to this the observation, that the down- 

 growing anlage of the infundibnlum not only divides this process of the 

 archenteron into an anterior and a posterior part, but that it also sub- 



