SPERMATOGENESIS OF PASSALUS CORNUTUS. 419 



going disintegration. In support of this view, he finds that they 

 appear at a time when the centrosomes are first set free and 

 often they may be found in close spatial relations to the centro- 

 somes. 



Whether or not the vacuoles and the cast-off portions of the 

 cytoplasm in Passalus correspond to the conditions described by 

 Voivnov in Cybister I am at present unable to say. The origin 

 of the vacuoles and their relation to the cytoplasmic buddings 

 can be best studied in the living material, and I shall leave the 

 question undecided here for lack of evidence. 



3. Maturation Divisions and the Spermatid. The spindles 

 developed for both maturation divisions are relatively very large, 

 both in actual dimensions and in number of spindle fibers. 

 Correlated with the large size of the spindles is the relatively 

 large nucleus, containing little chromatin but a large amount of 

 . karyolymph. The view of Conklin and others, that the spindle 

 grows at the expense of the karyolymph is certainly substantiated 

 in the case of Passalus. In both maturation divisions cell-plates 

 are developed which are very much smaller than those found in 

 the spermatogonia (Figs. 14, 8), and the remains of the spindles 

 persist for a considerable time after division. In the anaphase 

 of the second maturation division, the centrosomes are still 

 distinguishable lying close to the chromatin masses at the poles. 

 In the telophase of this division they are found lying on the 

 nuclear membrane. It is because of this position on the nuclear 

 membrane that they are not easily detected, but careful searching 

 and focusing will show their undoubted presence (Fig. 18). 

 Thus in the spermatid, the centrosome is still to be seen closely 

 attached to the nuclear membrane; it gradually shifts its position 

 until it comes to lie between the nucleus and the Nebenkern. 

 Usually there is a precocious growth of the axial filament (Fig. 

 19) before the centrosome arrives at its ultimate position. At 

 this time, the centrosome appears double, while the axial fila- 

 ment grows out between the two halves of the Nebenkern and 

 becomes associated with the latter in the formation of the tail, 

 as shown before (p. 413). As transformation continues (Figs. 

 21, 22), the centrosomes become more and more closely asso- 

 ciated with the nucleus, until in the older stages they are scarcely 



