MATURATION 133 



occur here are of a very special form, not found in the history 

 of other kinds of cells. These unusual mitoses are known as 

 the meiotic (maiotiCj Farmer and Moore) , or reducing divisions, 

 and their chief peculiarity consists in the fact that they result 

 in the formation of daughter nuclei containing the reduced 

 or haploid number of chromosomes. 



We shalTreview first the maturation of the spermatozoon, as 

 this is less modified than the ovum, from those conditions which 

 we regard as typical. Throughout the multiplication divisions 

 of the spermatogonia, the mitoses are all of the usual character, 

 except that the mitotic figures are relatively larger than in the 

 somatic divisions. The number of the chromosomes is the 

 same as in the somatic cells of the same organism; this is spoken 

 of as the diploid number. In many, perhaps most, organisms 

 the chromosomes differ from those of the somatic cells in form 

 and size characters, so that the germinal tissue can usually be 

 identified; the germinal tissue nuclei are in general larger and 

 richer in chromatin than those of somatic tissues, a difference 

 which, as previously noted, in a few forms (Ascaris, Cyclops, 

 some Teleosts) can be traced from very early cleavage stages. 

 But the constitution of the nuclei which pass into the inter- 

 kinesis after the last spermatogonial division, i.e., into the 

 primary spermatocyte nucleus, is essentially normal. Some- 

 times certain peculiarities become noticeable during the growth 

 period of these cells; the nucleus frequently does not remain in 

 the typical "resting" condition, but forms a more or less dis- 

 tinct spireme (leptonema, Winiwarter), and sometimes, even at 

 the beginning of this stage, there may be a fission of the chro- 

 matin granules, forming a sort of double spireme (Fig. 73). 

 At the close of this growth period, when the primary spermato- 

 cyte prepares to divide, the nucleus begins to show a very 

 unusual condition. The nucleus itself remains large, but the 

 chromatin, as it begins to form a spireme, in those cases where 

 this lias not formed previously, condenses at one side of the 

 nucleus, in the vicinity of the nucleolus, usually in the region 

 near the centrosomes and perhaps through their influence 

 (Schonfeld), into a dense mass in which little structure can be 



