392 MABOARET ROBINSON. 



short account of the formation of the blastoderm^ and 1900, 

 a longer paper on the development in the same journal. His 

 account of the formation of the blastoderm differs slightly 

 from Metschnikoff's. He says that the cleavage which he 

 observed was really intermediate between a discoidal cleavage 

 and a superficial one. In his second paper he again alludes 

 to this difference between his account of the formation of the 

 blastoderm and Metschnikoff's, and gives a short summary 

 of the development. 



Methods. 



The eggs were taken from the pouches and fixed in a hot 

 concentrated solution of corrosive sublimate to which a little 

 acetic acid was added. They were then washed and taken 

 very gradually through alcohols of increasing strengths up to 

 80 per cent. For their most excellent fixation and preserva- 

 tion I am very gi-ateful to Professor Weldon. 



The shells of the early stages were removed by teasing with 

 very fine sewing needles. 



As yolk preserved in sublimate is extremely brittle, in 

 order to cut it without its breaking I had recourse to the two 

 following methods : — (1) Embedding in celloidiu. (2) Paint- 

 ing each section with a mixture composed of equal parts of 

 gum mastic and celloidiu. 



The orientation was done in the first case by cutting the 

 celloidiu into the required shape, and in the second by fasten- 

 ing the embryo in position on a piece of lardaceous liver 

 before embedding in paraffin. The sections were cut with 

 Jung's microtome, and are 4 in in thickness. 



The embryos from which the surface views are taken were 

 stained with Delafield's ha)matoxylin ; the sections with 

 Klcinenberg's ha)matoxylin, and orange. 



The sections were all drawn under Zciss's objective d d. 

 and ocular No. 3 with Abbe's camera lucida, the details being 

 filled in with the help of a jY' immersion objective. 



