The Nervous System of Amblystoma. 439 



nearly as large as that of Necturus and the markings on the 

 neural plate are much more distinct. 



The abundance of eggs also makes Amblystoma punctatum a 

 good object for study, for, as Locy has already pointed out, in the 

 study of neuromeres a very large supply of material is essential. 

 In the vicinity of Hanover, N. H., the eggs are very common 

 in the early part of April, being found in large bunches in all 

 the small ponds and pools and even in the shallow ditches by 

 the roadside. In the years 1903, 1904 and 1905, between three 

 and four thousand eggs were collected for this study. 



In fixing the embryos several fluids were used, chromic acid, 

 picrosulphuric acid, Perenyi's fluid. All three of these fluids 

 proved to be useful for various purposes. For the study of 

 surface views chromic acid gave the best results. The eggs 

 after being dissected out of the main mass of jelly were dropped 

 into a 1 per cent solution. After remaining in this fluid for 

 about half an hour they were freed from the outer envelope 

 by the use of fine pointed forceps and needles and then trans- 

 ferred to a fresh solution of the same strength where they were 

 allowed to remain for about four hours. The material was 

 then thoroughly washed in running water for several hours and 

 finally transferred to 70 per cent alcohol. The alcohol was 

 changed as often as it became turbid. Before the eggs were 

 ready for study they were immersed for a few minutes in a weak 

 solution of eau-de-Javelle, which removed the inner membrane 

 and the last traces of any albuminous precipitate. This treat- 

 ment gave beautiful surface preparations. For dissection Per- 

 enyi's fluid was bei^ter. Aiter older embryos had been fixed 

 in this fluid for several hours and then hardened in 70 per cent 

 alcohol it was possible to dissect out the brain with fine needles 

 and sweep it clean with a delicate brush or the brain could be 

 dissected with the sense organs and the ganglia left attached to 

 it. For paraffin sections Kleinenberg's picro-sulphuric acid was 

 the most satisfactory for fixing embryos. 



The division of the embryos into a series of stages proved to 

 be a difficult task. A single set of eggs killed at one time con- 

 tains several stages, making it necessary to examine the eggs 



