IQ K. MITSUKURI; 



them round and round in very bright diffused light or in not too strong 

 direct sunlight until some one favourable position was secured. A 

 paper camera ohscura on the stage of the microscope cutting off light 

 from undesirable quarters and a. box of black wax in which white 

 embryos stood out clearly, I found of great help in studying details. 

 I also found that observations made on dark, grey skied days were 

 not good fov nuich, for I could invariably make out a great deal more 

 from the same embryos on clear bright days, or even earlier in the 

 nfternoon th;in later. Examination by reflected light Avas far more 

 useful than that by transmitted light. Staining was of little use, in 

 the study of surf ice-views, for that process obscured many of the finer 

 features. Great caution was necessary in arriving at negative conclu- 

 sions : for it proved highly unsafe to conclude that a structure did not 

 exist because it might not be visÜDle in one or two looks. A long and 

 careful study in the most favouraljle position and light was necessary 

 before coming to a final decision. As a matter of fact, many of the 

 embryos studied in the present investigation were some of those I used 

 when working out the fœtal membranes of Chelonia, (Contrih. II), but 

 many of the features which I describe in the following pages entirely 

 escaped me then and were therefore, not given in the figures accom- 

 panying Goutrih. II. 



In describino- the surface-chano-es, I find it most convenient to 

 treat the three species together in the earlier stages but to describe 

 them separately in their later stages. For while the course of develop- 

 ment is so much alike at first, Trionux shows from a certain stage on 

 considerable deviations from the other two, and these show some dif- 

 ferences amoni»- themselves. 



Earlier Stages 



I start with the Chelonia embryo to which the blastopore given in 



