The Spermatogenesis in Pentatoma up to the Formation of the Spermatid. (37 



chromatin nucleolus. The remaining 13 lie densely grouped in the 

 synapsis, and in the postsynapsis, when they separate from one another, 

 from 3 to 6 chromosomes can be counted, the number varying in dif- 

 ferent cells. In the rest stage the number cannot be determined. In 

 the succeeding dense spirem from 3 to 6 chromosomes again appear, 

 but shortly afterwards one or more of these chromosomes divide 

 transversely until the definitive number of chromosomes is produced, 

 namely 7. Thus the number of the chromosomes is reduced to less 

 than one half during the synapsis; whereas in other objects thus far 

 investigated it would appear that in the synapsis the number of 

 chromosomes is reduced exactly one half. Since less than one-half 

 result from the synapsis, and the number being a variable one (3—6) 

 we note the remarkable accommodation of these 3—6 chromosomes in 

 the prophase of the 1st reduction division, only so many of them seg- 

 menting transversely as to produce in all cases exactly 7 chromosomes, 

 i. e. exactly half the normal number. 



One of the original 14 chromosomes of the anaphase of the 

 spermatocytes becomes differentiated into a peculiar structure, which 

 has been termed a chromatin nucleolus; no such differentiation of a 

 chromosome has heretofore been described. This appears like a 

 nucleolus in the resting cell, but in the reduction mitoses divides ex- 

 actly like the true chromosomes. It is of the utmost importance to 

 determine what becomes of this structure in the spermatids: and also, 

 whether there is a corresponding differentiation of a chromosome in 

 the ovogenesis. It is very probable that a similar production of a 

 chromatin nucleolus will be found in other objects, if they be carefully 

 examined in regard to this point. Until further comparative studies 

 have been made, it would be premature to discuss the function of this 

 structure. 



Another peculiarity of Pentatoma is that there may be dis- 

 tinguished, from the synapsis stage on, two generations of spermato- 

 cytes, termed here the large and the small; the former differ from 

 the latter, as far as could be determined, merely in having a greater 

 amount of idiozomc substance, cytoplasm and nuclear sap. Though 

 the former cells have nearly double the volume of the latter, the 

 amount of chromatin is the same in both, and the development of both 

 is the same. These cells of the large generation cannot be compared 

 with the cells which produce the worm-shaped spermatozoa in Paludina, 

 since the number of generations in them and in the small generation 

 appears to be the same. 



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