Relation betzveen Nucleolus and Chromosomes. 47 



either that the plastin elaborated chromatin or more likely that chromatin 

 extracted from the nuclear reticulnm took lodgment there. The male pro- 

 nucleus exhibits a similar structure (fig. 85). In both pronuclei the plas- 

 mosome is lost shortly prior to fusion (fig. 86). All the evidence thus 

 points to a very intimate physical and chemical relation between the limn, 

 plasmosome, and chromatin nucleolus. I am inclined to the belief, in view 

 of my results, that these three substances simply represent different stages 

 in the process of elaboration of the same fundamental substance. 



In every full-grown oocyte are found usually one, some-times several, 

 masses of chromatin granules (figs. 31, 32, 33, 40). Generally these are 

 in close proximity to the nucleolus (fig. 41), but frequently also removed 

 at varying distances (fig. 38). Almost invariably this mass of granules 

 is on that side of the nucleus nearest the periphery of the oocyte (figs. 37, 

 49). In favorable cases I have been able to determine in it the character- 

 istic dumb-bell shape of the definite chromosomes, only somewhat reduced in 

 size. Again, in favorable sections I have been able to count approximately 

 1 8 such individual bilobed bodies (figs. 40, 43). There is no doubt that 

 these are the chromosomes which have persisted with identity unimpaired 

 all through the growth-period and are now taking their position in proxim- 

 ity to the nucleolus and periphery of the cell preparatory to maturation. 

 Occasionally the chromosome group or strand lies closely connected with 

 the nucleolus in the reticulum immediately surrounding it (figs. 37, 39, 41). 

 This gives the appearance of a union with the nucleolus. Conklin (1902) 

 describes very similar conditions in the maturing egg of Crepidula. It is 

 doubtful if the chromosomes ever penetrate within the nucleolus, but they 

 do often come into very close connection externally. In this state one can 

 often see a portion of the mass extending beyond the border of the nucleo- 

 lus, simulating an extrusion from the latter. Mathews (1895) mentions 

 the presence of such a mass of granules in Asterias forbesii, but beyond 

 saying that it gives rise to the chromosomes of the first maturation spindle 

 gives no further details. Bryce (1901) ventures the suggestion concerning 

 a similar mass of granules in Echinus that it may possibly represent synapsis. 

 Tennent (1906), on the other hand, suggests on the basis of experiments 

 on eggs of Asterias forbesii subjected to CO 2 treatment and subsequently 

 fertilized that " a conjugation or synapsis of egg chromosomes and sperm 

 chromosomes takes place immediately before the formation of the equatorial 

 plate of the first segmentation spindle" (p. 539). Judging from analogy 

 with other forms where synapsis has been definitely observed, and on the 

 strength of appearances in the youngest oocytes which seem to agree with 

 the descriptions of early postsynaptic processes in some of these forms, I 

 believe that in Asterias also true synapsis occurs some time during the telo- 

 phase of the last oogonial division. The results above reported, I believe, 

 justify the interpretation of this mass of chromatin granules as the persist- 



