A SOUTH AMERICAN SPECIES OF PERIPATUS. 351 



cells in which cell outlines can only with great difficulty be 

 distinguished. 



These embryonic cells have a very peculiar appearance, due, 

 as it seems, to the diffusion of the nuclear substance or chroma- 

 tin throughout the cell substance ; it therefore follows that 

 no definite nucleus can be detected. Careful focussing, however* 

 seems to indicate clear lines of protoplasm where no chromatin 

 is present, and these lines of clear protoplasm seem them- 

 selves to demarcate the various cells of which the embryo is 

 made up. 



In the next stage the embryo is still sessile, that is, it is 

 attached to the vesicle wall along its whole length. 



Fig. 12 represents an embryo of about this stage, measuring 

 about '1 mm. across, lying in its vesicle, the vesicle again lying 

 in the cavity of the uterus ; the two latter have been split open* 

 so as to expose the embryo. 



Figs. 9 a and 9 b represent two sections, an embryo and vesicle, 

 of approximately the same size and age as fig. 12 ; the embryo 

 •14 mm., the vesicle *28 mm. in diameter. 



The vesicle wall (v. w.) is rather thicker in this stage, and 

 the individual cells composiug it are very much better defined 

 than in the previous stages. The embryo proper consists, as 

 before, of large cells with diffused chromatin and obscure cell 

 outlines, and of supporting cells (sp. c), whose nuclei stain 

 very deeply, and whose cell outlines are invisible. 



Between the two forms of cells of the embryo there has now 

 appeared a cavity (o). This I believe to be arti-fact, and due 

 to the action of reagents, especially as it is very inconstant in 

 its appearance in embryos of this stage. 



The only other noticeable feature of this stage is the so- 

 called amnion (am.) of Kennel ; this consists in the region of 

 the embryo of a few scattered nuclei embedded in strings of 

 protoplasm, in some cases surrounding and fusing with the 

 embryo, in others fusing with the vesicle wall. 



Fig. 9 b represents a section of the same vesicle behind the 

 embryo proper. Here a complete ring of nucleated protoplasm 

 is seen surrounding the space where farther forward would be 



VOL. XXVIII, PART 3 NEW SER. B B 



