Papers from the Marine Biological Laboratory at Tortugas. 233 



companled by the gradual degeneration of the nucleus. It seems to be not 

 unlikely that these two facts stand in a causal relation to each other. 



The same condition, that is, the unrepeated secretory activity of the 

 cell accompanied by the degeneration of the nucleus, holds true in the case 

 of the apyrene spermatozoa of Strombus as well as in the nurse-cells of 

 Littorina. But here the question might well be asked, why does not the 

 nucleus degenerate directly, instead of undergoing the complicated history 

 that has been described? The primary function of the nucleus is concerned 

 first with the growth of the spermatoblast and then with the secretion of 

 the albuminous bodies, and possibly its presence is essential for the develop- 

 ment of the great centrosome with its many centrioles. The differenti- 

 ations which occur in connection with the centrioles lead to the formation 

 of the undulating membranes and they are initiated by the disappearance 

 of the centrosome. It is believed that the impulse, whatever it may be, 

 which is responsible for the disappearance of the centrosome causes also the 

 dissolution of the nuclear membrane. That impulse may be the same as 

 that which causes a cell to divide mitotically, but, as has been shown, there 

 is no real evidence to support such an assumption. Stated a little differ- 

 ently, when considered in regard to the subsequent development of the 

 apyrene spermatosome, it is the change that occurs to the centrosome that 

 is of prime importance at this time and that which occurs to the nucleus is 

 incidental to it. 



Were this not so, we should expect either that the chromatic fragments 

 would degenerate without first becoming vesiculated and the secretion of 

 the albuminous bodies be commenced at the same time, as is the case in the 

 apyrene spermatozoa of Vermefus,^ or else that the nucleus would remain 

 intact until the secretory activity of the cell is begun and then degenerate 

 as a whole, which is the case in the nurse-cells of Littorina. Instead, the 

 karyomerites become vesiculated and form a great number of secondary 

 nuclei which increase in size until the first albuminous bodies are formed, 

 when they begin to degenerate. Moreover, if the secretory activity of the 

 cell is enhanced by an increase in the surface contact between the nucleus 

 and the cytoplasm, then the formation of the secondary nuclei is of great 

 advantage. 



The conditions observed in the seminal receptacle and uterus of Strombus 

 bituberculatus and S. gigas after copulation and at a time before oviposition 

 has commenced, and indeed before the ova are fully matured, throw a 

 certain amount of light upon the nature of their function. The fact that 

 eupyrene spermatozoa are found in those parts at such a time indicates that 

 they, or at least some of them, must remain there for a protracted period 

 that is, until and during the time of oviposition. The greater part of that 

 time is no doubt spent in the seminal receptacle, where they can and do 

 receive an independent supply of nourishment. But, judging from the 



1 In this connection Kuschakewitsch ('13) has made the suggestion that in Vermelus the retention of the 

 chromatic elements as such almost until the end of spermatogenesis is to be explained on the grounds that the 

 chromatin participates in the formation of the albuminous bodies in the protoplasm of the apyrene spermatozoon. 



