122 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



tocytes support in many particulars the old hypothesis of division by 

 fibrillar contraction. 



In both types of spermatocyte the centrosome is the small, inner, deeply 

 staining body at the centre of the aster. The larger more diffusely stain- 

 ing structure surrounding this — the centrosphere — varies greatly in size 

 and appearance in different stages of mitosis, and shows at various times 

 that it is merely a reserve supply of archoplasm, which is used as occasion 

 demands in the formation of the astral rays. 



Metamorphosis of the spermatids. — The spermatids derived from 

 the two type* of spermatocytes produce spermatozoa differing in no 

 observable particular except that of size. They are probably all 

 functional. 



2so true Nebenkern exists in Scolopendra, as the remnants of the spin- 

 dle are cast out of the cell in the telophase of the preceding division. In 

 later stages of metamorphosis there arises from a portion of the archo- 

 plasm a structure which is comparable to the Faserkorb found in the 

 spermatogenesis of mammals. 



In the process of lengthening, the spermatid first assumes an amoeboid 

 appearance, and later elongates in the direction of least resistance. 



Tlie axial filament arises in close relation with the centrosome, but not 

 from centrosome substance. There is considerable evidence pointing toward 

 its origin from archopdasm. 



Soon after the appearance of the first fundament of the axial filament, 

 the centrosome breaks up, usually into three parts. One of these retains 

 its positions at the proximal end of the filament, whereas the others take 

 up positions at equal distances from the first and upon opposite sides 

 of it. 



After the cell has begun to lengthen the lateral centrosomes enter the 

 nucleus, where they come to be connected with the median centrosome by 

 means of fibres. This relation is retained throughout all later stages of 

 metamorphosis and in the mature spermatazoon. 



The acrosome arises from a number of small spherules of archoplasm, 

 which become vesicular and soon fuse to form a large club-shaped ves- 

 icle ; this comes to lie with its narrower end in contact with the anterior 

 end of the nucleus. In later stages of metamorphosis it lengthens out 

 into a long, slender pointed filament. 



The chromatin of the spermatid undergoes a chemical change whereby 

 it loses its affinity for chromatin stains. Later, in the spermatozoon, the 

 chromatin reappears in an apparently amorphous condition, being de- 

 posited at the periphery of the elongated head. 



