68 THOS. H. MONTGOMERY jr., 



The observations furnish no strict proof of the permanence of the 

 centrosomes. They are not to be seen in the resting spermatogonia, 

 but are found in the prophases of mitosis in the idiozome, out of 

 which they subsequently pass. In the anaphase of the 1st spermato- 

 cytes one or two small granules of equal size are seen with such re- 

 gularity in the idiozome, that they must be considered centrosomes; 

 their duplicity would show that the centrosome divides in the anaphase, 

 or in the metaphase of the last division of the spermatogonia. In 

 the resting spermatocytes it is difficult to find them, owing to the 

 granular structure of the idiozome substance. In the prophase of the 

 1st reduction division the two centrosomes wander to opposite sides 

 of the nucleus, when each immediately divides into two, — a case of 

 very early division. 



In the spermatogonic divisions the primary central spindle per- 

 sists during the mitosis: but in the reduction divisions three succes- 

 sive central spindles are produced, apparently without genetic connec- 

 tion with one another. 



The idiozome takes apparently no part in the formation of spindle 

 fibres. Since it increases in amount especially in the growth period 

 of the spermatocytes, and is more voluminous in cells of the large 

 generation, it might represent some metabolic substance connected 

 with process of nutrition; but if this were the case, since the centro- 

 somes he within it, the latter might be considered to be agents in 

 the process of nutrition, as well as being the chief mechanical centres 

 in mitosis. 



III. 

 Greneral considerations. 



Nearly every contribution dealing with spermatogenesis or ovo- 

 genesis discusses also the theoretical interpretation of the phenomena 

 observed, and in not a few cases the speculations occupy as many 

 pages as do the observations. On account of this already crowded 

 state of the theoretical market, I have hesitated to publish my own 

 theoretical conclusions, being fully convinced that the few morpho- 

 logical facts which we have do not warrant the building of a theore- 

 tical superstructure. But I wish to lay emphasis on the question — 

 what is a chromosome? Should every separate chromatin element 

 be termed a chromosome, or only an element of a particular mode 

 of formation? 



The two reduction divisions cannot be taken as the starting point 



1 



