REMARKS ON THE DEVELOPMENT OP AMPHIOXUS. 361 



gave evidence of thorough preservation ; and in such of my 

 material as was not preserved in osmic acid the limits of the 

 vai-ious cavities could not be made out, since shrinkage of 

 ectoderm and mesoderm and the swelling of the gut cells had 

 obliterated them. 



With regard to Klaatsch's second remark, I can only 

 interpret it as an insinuation that I wilfully distorted facts 

 in order to make the development of Amphioxus harmonise 

 with that of Balanoglossus. Such an insinuation I most 

 emphatically repudiate. It is perfectly true that I have long 

 regarded the structure of Balanoglossus as likely to give the 

 best clue to Vertebrate ancestry, and that I was convinced 

 that a careful examination of the early development of 

 Amphioxus would reveal agreement in the essential plan of 

 development of the two types. But the manner in which this 

 agreement manifested itself was a surprise to me. 



I commenced by investigating Hatschek's nephridium in 

 the older larva, and I was astounded to find that it was in 

 continuity both with the alimentary canal and the cavity of 

 the first myotome. I then, by examining successively younger 

 stages, traced this connection back to the embryo, and found 

 there the first mj'otome on either side was in communication 

 with the gut cavity when no other myotome opened into the 

 endoderm. This was seen in all the embryos of this age 

 which I examined. 



I then made the discovery that no other myotome, in the 

 strict sense of the word, is ever in open communication with 

 the gut, but that one always finds at the hinder end of the 

 animal on each side a dorso-lateral groove or evagination of 

 the gut wall, from which fresh myotomes (somites) were 

 successively cut off as the animal grew in length. I may 

 remark that this view of the origin of the bulk of the meso- 

 derm is not only in accordance with the results of the latest 

 work on the origin of the mesoderm in Vertebrata, but, as 

 Mr. Sedgwick was kind enough to inform me, it was in 

 accoi-dance with the results of his own unpublished observa- 

 tions on Amphioxus, 



