154 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY, 



I. Locy's "Neural Segments" or " Metameres." 



a. Material. 



Much of my material was collected with a view to the study of the 

 "neural segments" or "metameres" described by Locy ('94 and '95). 

 In a preliminary paper, which appeared with numerous illustrations in the 

 " Anatomischer Anzeiger," 1894, Locy affirmed the discovery of "neural 

 segments " in embryos of Squalus acanthias ^ at stages preceding the 

 formation of the medullary folds and " before the mesoblast has, to any 

 extent, become divided into somites." He therefore believed that these 

 " epiblastic segments must be independent of any formative influence of 

 the segments of the mesoblast." This discovery is interesting, and, if 

 confirmed, one of most fundamental importance. I have therefore col- 

 lected a large number of Squalus embryos in early stages of develop- 

 ment, in order to confirm, if possible, Locy's results. 



S. acantliias is abundant along the coast of Massachusetts in early 

 summer, and the embryos are very easily obtained. My collecting was 

 done at Rockport, Massachusetts, during the months of July and August, 

 1894, 1895, and 1896, and the number of specimens obtained exceeds 

 twenty-five hundred. Locy has well insisted on the necessity of abun- 

 dant material in closely connected stages of development. 



The killing agents which I have used were (1) DavidoS's corrosive 

 sublimate-acetic; (2) Kleinenberg's picro-sulphuric (undiluted); and (3) 

 a mixture of Kleinenberg's picro-sulphuric (1 vol.), with ^^ chromic 

 acid (3 vol.), especially recommended by Locy. 



In this material were more than two hundred and fifty embryos 

 corresponding to Balfour's stages C, D, and E. The specimen which 

 shows Locy's " neural segments " best was killed in Kleinenberg's picro- 

 sulphuric mixture (Plate 1, Figs, 1 and 2). I cannot recommend the 

 mixture composed of picro-sulphuric and chromic acids, since specimens 

 killed in it were not well preserved histologically. DavidoS''s corrosive 

 sublimate-acetic seems to me the best for general purposes of all the 

 killing agents I have used, and consequently most of my material has 

 been so killed. For the special study of the development of the nerves 

 and the fibre courses in the wall of the brain, I have used material killed 

 with vom Eath's fluid, followed by pyroligneous acid. This method I 

 regard as most valuable, since with it nerve fibres are differentiated by 



1 Squalus acanthias (Linnaeus, 1748), synonymous with Acanthias vulgaris 

 (Risso, 1826). 



