348 W. L. SCLATER. 



it. The nuclei of the uterus stain much more darkly than the 

 nuclei of the embryo itself. 



In fig. 3 the only striking peculiarity is the presence of the 

 two bodies (p. b.); it seems possible that these may be polar 

 bodies, though beyond their appearance and position I have no 

 further evidence to offer. 



Kennel has also figured these early segmenting embryos, 

 and my results do not differ materially from his ; he has also 

 figured what he believes to be polar bodies, but in no case do 

 they seem to have separated from the embryo itself, but 

 remain still buried in its substance. 



The next stage, which is represented in fig. 6, presents a con- 

 siderable difficulty ; it seems to resemble in some respects 

 fig. 51, PI. viii, of Kennel. 



This embryo ('105 mm. in diameter), which at first I took to 

 be a vesicle with the embryo inside, must, I think, be 

 regarded as a stage previous to the one next to be described, 

 i. e. the pseudogastrula stage. 



The embryo consists of a single layer of cells marked out 

 from one another only by their nuclei ; it is approximately 

 spherical. The nuclei on one side of the embryo, on being 

 traced out, are found to form a small patch on that side of the 

 sphere, and are considerably larger and more numerous, and 

 it is at this spot, I take it, that invagination will take place. 



That this embryo must be placed at this point in the series 

 is evident from the size ; as the embryos hitherto described 

 varied from '0-i mm. to *08 mm. in diameter, this one (i. e. 

 fig. 4) is "105 mm. in diameter and approximately spherical, 

 while the pseudogastrula, to be described below, is *112 mm. in 

 diameter and # 190 mm. in length ; this of course forms a 

 fairly regular gradation of increase in size. 



The ovum, therefore, of Peri pat us imthurni is holoblastic, 

 and the segmentation is fairly regular, the result being a 

 blastosphere (fig. 6), that is, a hollow vesicle one cell thick. 

 There is no sign of any attachment of the embryo to the wall 

 of the uterus, and the inner wall of the uterus is marked by a 

 thickened and crinkled line, which is very characteristic, and 



