202 BULLETIN OF THE 



those employed by them. The researches of these authors had been 

 conducted on Mammalian material only, and it was the hope of the writer 

 to find in Amphibia a similar mode of origin for the excretory duct. 



The material employed in the present investigations consisted of em- 

 bi-yos of liana, Bufo, and Amblystoma. The study of the problem was 

 begun with Rana pipiens Schreb. (halecina), embryos of which had been 

 prepared in the spring of 1884 by Prof. E. L. Mai-k, who kindly placed 

 his series at my disposal. In the spring of 1889, while in Baltimore, 

 Md., I secured an abundance of the eggs of Rana sylvatica Le Conte.^ 

 These eggs are large, measuring at the blastula stage two millimeters or 

 more in diameter. I also found them far better for embryological study 

 than those of other species of frogs examined. An advantage which 

 they possess for my purpose is that the germ layers are very well sepa- 

 rated from one another. Moreover, the body cavity appears at an early 

 stage, making the boundary between the somatic and the splanchnic 

 mesoderm very pronounced, both in the region of the protovertebrse and 

 of the lateral plates. 



The eggs of Bufo studied, B. americanus Le Conte, were collected dur- 

 ing the spring of 1887, in Cambridge and in Jamaica Plain, Mass. At 

 this time I also collected a small quantity of Amblystoma eggs from a 

 pond in Jamaica Plain ; but a careful search, carried on during several 

 subsequent trips to this locality, failed to yield any more eggs. 



Prof. J. S. Kingsley at this time kindly sent me from Indiana some 

 Amblystoma material which he had preserved ; but for the determina- 

 tion of many points at issue I was obliged to wait till another season 

 offered opportunities for collection. In the spring of 1889, therefore, I 

 made a trip to Baltimore, where I was able to collect an abundant sup- 

 ply of the eggs of this Amphibian, most if not all of the material col- 

 lected belonging to the species A. punctatum Linn. In this work I was 

 accommodated at the Biological Laboratory of the Johns Hopkins Uni- 

 versity, — a privilege for which I am under obligation to that institu- 

 tion. My thanks are particularly due my friend Dr. T. H. Morgan for 

 his kind assistance during my stay in Baltimore, and for material of his 

 collection. 



I may here also express my obligations to Dr. John S. Billings, Sur- 



1 Inasmuch as the observations of European investigators have usually been 

 made on K. temporaria, it is of interest to note that K. S3'lvatica Le Conte has been 

 regarded by some systematists as a varietj- of R. temporaria (Giinther, '58, p. 17). 

 In any event, the development of the two forms may be assumed to be very 

 similar. 



