The Spermatogenesis in Pentatoma up to the Formation of the Spermatid. 65 



In all follicles the spermatogonia are of the same size. About the 

 stage of synapsis the spermatocytes of the large generation commence 

 to grow in size more rapidly than those of the small, and their 

 larger size is due to greater increase in the amount of the cytoplasm, 

 idiozome substance and nuclear sap ; the amount of chromatin is the 

 same in spermatocytes of both generations. In the cells of the large 

 generation the processes of the reduction divisions are exactly the 

 same as in the cells of the small generation, except that in the former 

 the cells are larger, 



9) The 1st spermatocytes attain their greatest size in the rest 

 stage : the growth period extends from the synapsis to the rest stage. 

 The chromatin at this period forms an irregular network, in which 

 individual chromosomes cannot be distinguished. The chromatin 

 nucleolus contains a clear, fluid globule, which is probably not a 

 derivative of its own substance; the true nucleolus has attained its 

 greatest dimensions, and is attached to the chromatin reticulum. The 

 idiozome substance has increased in amount, and forms a cap sur- 

 rounding the nucleus on nearly all sides ; centrosomes could be found 

 in it in only a few cases, and then two to each cell. 



10) In the prophase of the 1st reduction division the chromatin 

 reticulum shortens, and condenses into from 3 to 6 long loops (dense 

 spirem stage), the number of the loops varying in different cells: at 

 no stage is a continuous spirem thread formed; there are thus as 

 many chromosomes as occurred in the preceding postsynapsis. The 

 3 — 6 chromosomes shorten and thicken (loose spirem stage), and as 

 they do so one or more of them (according to their number) segment 

 transversely until the 7 definitive chromosomes are formed. Occasionally 

 the latter are ring-shaped, but even then these rings have usually the 

 value of a single chromosome each. The 7 chromosomes shorten still 

 more (they show marked dimensional diiferences), and finally, before 

 the nuclear membrane has disappeared, all become dumbbell-shaped, 

 with a transverse constriction; this constriction is often apparent 

 before they have shortened. At no stage in either of the reduction 

 mitoses is there any evidence of a longitudinal splitting of the chromo- 

 somes. The chromatin nucleolus has become much smaller, due to a 

 dissolution of a portion of its substance, and is much smaller than 

 any of the chromosomes, but like them it shows a transverse con- 

 striction before the disappearance of the nuclear membrane. In the 

 spirem stages two centrosomes appear, connected by a central spindle 

 (primary central spindle) ; before the centrosomes reach opposite poles 



Zool. Jahrb. Xlt. Abth. f. Morph. K 



