No. I.] THE EMBRYOLOGY OF UMULUS. 39 



the moment of killing excellent, but evanescent, surface views, 

 as a short immersion in alcohol renders the whole surface 

 one uniform color. Hence, in order to orient these eggs for 

 subsequent section, I marked each one, at the moment of killing, 

 with India ink — not affected by alcohol — and subsequently- 

 arranged the Q^'g with reference to the line thus afforded. For 

 staining I used chiefly alum cochineal and Grenacher's borax 

 carmine, while a short stay in osmic acid brought out certain 

 details. 



I found it impossible to cut the early eggs in paraffin. 

 Absolute alcohol and the clearing reagents rendered the yolk 

 extremely hard and brittle, while the paraffin refused to pene- 

 trate the centre of the ^gg. So for the early stages I had 

 recourse to celloidin. For the main outlines of the process 

 employed I am indebted to the suggestions of Dr. H. C. Bum- 

 pus. The celloidin was hardened with chloroform and cleared 

 with origanum oil or with a mixture of turpentine and carbolic 

 acid before cutting. The sections were cut with the knife 

 flooded with the clearing fluid, and then placed in order on 

 the slide. Being already cleared, all that is now necessary is 

 to apply balsam and the cover glass. In many respects this 

 process is identical with that described by Eyclesheimer ('90). 



To study the stages after the outlining of the germ, the 

 chorion was removed by needles,^ and then by careful manipu- 

 lation the blastoderm was stripped from the yolk, stained, and 

 either mounted in toto for surface views or sectioned as usual in 

 paraffin. In the later stages the processes of development so 

 modify the yolk that the whole embryo is capable of being sec- 

 tioned in the usual manner. 



As a result of the difficulties of manipulation the following 

 account of the early stages is exceedingly fragmentary, yet it is 

 hoped that the little here detailed will prove of value, especially 

 as almost nothing is known of the processes involved in the 

 formation of the germ layers. (See Postscript.) 



^ Owing to the great thickness of the chorion I found it difficult to control the 

 action of eau de Javelle or Labbaracque's solution. Before the chorion was dissolved 

 the solution would frequently affect the egg, interfering with staining and making it 

 very crumbly. 



