154 KANSAS UNIVERSITY QUARTERLY. 



be seen in the anaphase, indicating a tendency of the nuclear lymph 

 to accumulate in a zone around each of the chromosomes. 



Now, in this case, instead of an aggregation of karyoplasm into a 

 single mass and a general separation of the chromomeres before the 

 formation of the nuclear membrane, the differentiation of the sepa- 

 rating layer between cytoplasm and karyoplasm must begin before 

 the chromosomes become attingent at the poles. The result is a sepa- 

 rate membrane around each of the little aggregations of nuclear 

 plasm, and consequently around each of the chromosomes. 



At this stage, we have a condition in which any interchromosomic 

 exchange of ids is a physical impossibility, and, if we follow the de- 

 velopment further, we will be confronted by conditions strongly in- 

 dicative of the continued maintenance of the individuality of the 

 chromosomes. It is true that soon after the meeting of the chromo- 

 somes at the poles dissolution of the contiguous parts of all but one 

 of the vesicles takes place, so that the lymph of one may pass freely 

 to the other; but throughout the whole process of formation of the 

 spiremes, the threads of the different compartments of the nucleus 

 never get in such relations with each other that it would be possible for 

 an id from a given point of one to pass in a straight line to any but a 

 very limited portion of any other. If, therefore, an attraction be 

 postulated between ids of different chromosomes, it would be difficult 

 to see how, by means of the forces now known, or believed, to be 

 present in cell nuclei, an id from the blind end of one of the dilations 

 of the nucleus will ever be able to reach its miitually attracting id in 

 the blind end of another. I may say in connection with this point 

 that the period of complete diffusion, when the interchange might 

 be conceived to be facilitated by currents within the nucleus, is so 

 short that I have been able to find in all my material but a very few 

 cells showing it. 



It would be difficult to imagine by what complex laws of attraction 

 a rearrangement of chromomeres or of ids could take place through 

 the tortuous channels of the nucleus which would result in the origi- 

 nal number of chromosomes, one and only one lying in each of the 

 compartments of the nucleus. 



I would conclude, therefore, that the changes of the nucleus of the 

 .secondary spermatogonia are purely metabolic in their nature, and 

 that the individuality of the chromosomes is maintained. 



SUMMARY. 



1. The testis is unpaired and is composed of short, thick follicles 

 emptying into a common collecting duct, which, in turn, is connected 

 with the vas deferens. Inside the follicles of the adult testis, the 

 spermatozoa may be found in large numbers at the end nearest the 



