THE DEVELOPMENT OF THE EYE MUSCLES IN ACANTHIAS/ 



BY 



ARTHUR B. LAMB. 



From the Biological Laboratories of Tufts College. 



With 9 Test Figukes. 



These studies were imdertaken at the suggestion of Dr. J. S. Kings- 

 ley and were carried on during the year 1899-1900 under his direction, 

 at the Biological Laboratory of Tufts College. 



My specimens were killed either in aqueous corrosive sublimate or in 

 Davidolf's corrosive-acetic mixture. Dektield^s hematoxylin was prin- 

 cipally used as a staining agent. Wax reconstructions were made ac- 

 cording to the method of Born. My results are largely but confirma- 

 tory of those of YdiW Wijhe, Miss Julia Piatt, Hoffmann and Neal. 

 It is hoped, however, that a presentation of the subject freed from 

 externals may, together with the series of reconstructions submitted, 

 assist in the comprehension of the process of development. 



The discovery that m selachii the eye muscles are developed from 

 the epithelial walls of the Ist, 2nd and 3rd head somites was made by 

 Marshall. His results have been repeatedly confirmed, and there can 

 be no reasonable doubt of their validity. I use the term " somite " 

 advisedly, being convinced that in Acanthias the head cavities are 

 comparable with trunk somites. Neal, 98, p. 187, presents an excellent 

 summary of the evidence on this point. A history of the development 

 of the eye muscles is therefore a history of the origin and differentia- 

 tion of these head somites. At this point I wish to call attention to 

 the very detailed accoimt of the early history of these somites, pre- 

 sented by Hoffmann, 96, in his " Embryology of the Selachii." 



AxTERiOR Somite. — Before passing to a consideration of the eye 

 muscle somites proper. I propose, for the sake of completeness, to con- 

 sider the anterior somite. Van Wijhe saw (82, p. 13), in the single 

 specimeu of Galeiis at his disposal, on either side of the head, anterior 

 to the 1st or premandibular somite, a slender cavity with distinct and 



1 Studies from the Biological Laboratories of Tufts College, under the direction of 

 J. S. Kingsley, No. XXIX. 



