A SOUTH AMERICAN SPECIES OP PERIPATUS. 217 



form. The difference in size between the youngest embryo (a 

 sphere measuring "04 mm. in diameter) and the fully formed 

 one, which is often an inch long, is enormous, and there must 

 be a very large quantity of food material absorbed in order to 

 account for this increase in size. This food material must 

 necessarily be derived from the uterine walls, and it appears to 

 me that it is principally derived from these vacuolated regions, 

 and that the pigment and the structureless protoplasm figured 

 X are concerned in this phenomenon. 



III. Details op the Development. 



The youngest embryos I have found are all of approximately 

 the same age and are in the segmenting stage, but owing to 

 their small size I have never been able to get them, except in 

 a series of sections of unsplit uterus ; and in this case the 

 embryo is never so satisfactory, owing probably to the contrac- 

 tion of the uterine tissues due to the action of the reagents. 



Fig. 2 represents what I take to be the youngest of all in 

 the segmenting stages ; it measures "04 mm. across. It is not 

 easy to assert definitely, but it probably contains eight nuclei 

 embedded in a mass of unsegmented protoplasm, the whole 

 lying free in the cavity of the uterus, which is always present 

 where the embryo is, and for a short distance on either side 

 of it. 



In fig. 4, which represents an embryo ('07 mm. in diameter) 

 at a rather more advanced stage, the cells — or rather the nuclei, 

 since there is as yet no sign of any cell partitions — have begun 

 to arrange themselves in a ring round a central cavity. This 

 embryo probably consists of twenty-four cells or rather nuclei. 

 This embryo was also peculiar in that the uterus did not have 

 the masses of pigment usually found in it on either side of the 

 embryo. This embryo measures "08 mm. long by '07 mm. 

 across. 



Figs. 3 and 5 are approximately of the same age as fig. 4. 



In fig. 5 the uterus has been drawn on one side to show the 

 usual arrangement of the nuclei of the uterine epithelium; 



