MONOGRAPH OF THE EXISTING CRINOIDS. 361 



eight or nine chromosomes surrounded by a lightly staining caryoplasma. Hence 

 it is probable either that the chromosomes in the nucleus of the spermatozoon 

 dissolve in the caryoplasma and form a denser homogeneous mass preparatory to 

 penetrating the membranes and more compacted outer cytoplasmic layer of the 

 ovum, or else the caryoplasma is extruded and the nucleus of the mature spermato- 

 zoon consists very largely or even solely of chromosomes (nuclein) closely packed 

 together. 



There is a very considerable reduction in the size of the nucleus in changing 

 from that of the spermatic! to that of the spermatozoon, and correspondingly an 

 increase in size, with a reappearance and wider separation of the same number of 

 chromosomes, after the spermatozoon in the fertilization process has passed the 

 peripheral denser portion of the cytoplasm of the ovum. The question is, whether 

 this change in the nucleus is merely one of density; that is, does the nucleus of 

 the mature spermatozoon consist of the same quantity of nuclein and caryoplasma 

 but with the nuclein dissolved in the caryoplasma, or does the caryoplasma as a 

 liquid portion pass into the cytoplasm before the spermatozoon becomes fully 

 mature, and after the spermatozoon has entered the cytoplasm of the egg is the 

 caryoplasma restored from the cytoplasm of the egg ? 



On account of the very evident alterations in size of the nucleus one is inclined 

 toward the latter alternative. It seems to be a pretty good case for proving that 

 an interchange of substance goes on between the nucleus and the cytoplasm, and 

 that in this instance at least the substance which passes through the nuclear mem- 

 brane is the caryoplasma, a liquid protoplasm. If this is the case it makes strongly 

 for the view that the nuclein is the essential part, for in this case most of the male 

 caryoplasma passes out into the cytoplasm of the male cell, and the caryoplasma 

 is replaced by liquid from the cytoplasm of a female cell. 



In Antedon the nucleus is comparatively small ; in the anterior surface, usually 

 at the very apex, there is a depression into which the centrosome fits. 



Field has never seen a centrosome in the spermatogones in the outer zone 

 that is, next to the germinal epithelium. He first succeeded in finding it in the 

 dividing spermatogones. At first it seemed to be within the nuclear membrane, 

 but observation on this point was very difficult, and he is by no means positive in 

 regard to the place or manner of first appearance. 



Field never saw in the spermatogone the actual division of the centrosomes, 

 but it is probable that it occurs preparatory to the mitotic division. With the 

 disappearance of the nuclear membrane the centrosomes are seen to have the usual 

 position at the poles of the nuclear spindle. 



This spindle seems to be formed of those violet staining granules which are 

 present in the nucleus before the disappearance of the nuclear membrane. These 

 granules remain in close proximity to the chromosomes, the cytoplasm beinw 

 entirely free from them previous to the final division which gives rise to those 

 cells, the spermatids, which will become the spermatozoa. 



After the division of the nucleus of the spermatocyte into the two spermatid 

 nuclei, and before the division of the cytoplasm has taken place, those granules 



