No. I.] POLYCHOERUS CAUDATUS. S5 



the undertaking. Also, it would have been desirable to have 

 followed the history of the centrospheres and centrosomes into 

 the segmenting ovum, but as related elsewhere (10), great diffi- 

 culty was experienced in getting sections of ova after they had 

 been inclosed in their gelatinous capsules. In nuclei in which 

 the nucleolus had broken down and begun to disintegrate, I 

 have noticed in two different cases, out of the many hundred 

 examined, adhering to the inner side of the nuclear wall and in 

 close proximity to the fragments of the nucleolus, a small, clear 

 vesicle which strongly resembles the primitive archoplasmic 

 vesicle as it appears in Fig. 9 outside of the nucleus. This 

 would indicate an intra-nucleolar origin for this body. The 

 substance of the nucleus in which this body is imbedded is, 

 however, so dense and stains so deeply that it is impossible to 

 be certain of this observation. The structure which I describe 

 may or may not be the primitive centrosphere. 



It is therefore possible that in this form, as in Asieris as 

 described by Mathews (14), the centrosphere is developed and 

 remains within the nucleus until the ovum is fully matured. 

 The fact that at this time the nucleolus disintegrates suggests 

 that the centrosphere may have been located within this dense 

 mass. Although I have devoted much study to this point I 

 have not been able to demonstrate whether the centrosphere 

 actually migrates from within the nucleus or whether it origi- 

 nates in the cytoplasm. 



I have sought in vain in young and almost mature ova for 

 some trace of this body or of a centrosome. The most careful 

 examination of serial sections, double stained with iron alum 

 haematoxylin and with Bordeau red or orange G, fail to dif- 

 ferentiate any such structure. If it exists in the cytoplasm, it 

 must be exceedingly minute, or else does not at this stage 

 respond to the same stains as it does later, and therefore must 

 be of a different chemical structure. 



When first seen the centrosphere is a small, dark-walled 

 vesicle with a few short rays projecting in all directions (Fig. 9). 

 The center of this vesicle is quite clear and stains red with 

 Bordeau red or yellow with orange G. At this stage there is 

 no centrosome or speck of any kind within the vesicle. Still 



