66 THOS. H. MONTGOMERY jr., 



of the nucleus this spindle appears to disappear. When the centro- 

 somes have reached opposite sides of the nucleus, each of them 

 divides into two, but the two halves of each remain connected by a 

 centrodesmosis. The nuclear membrane is projected outward towards 

 each pair of centrosomes, in the form of a little cone, within which 

 lies a mass of substance probably derived from the true nucleolus. 

 Pole rays are now well developed. 



11) The nuclear membrane disappears, and from each pair of 

 centrosomes pass two mantle fibres (probably of nuclear origin) to 

 each chromosome; the chromatin nucleolus still persists, and like the 

 chromosomes has two mantle fibres attached to each of its ends. A 

 secondary central spindle is formed. The 7 chromosomes and the 

 chromatin nucleolus are pulled into the equator of the spindle where 

 they lie with their long axes parallel to the axis of the spindle, and 

 their constrictions transverse to it. 



12) In the metakinesis of the 1st spermatocytic division each of 

 the 7 chromosomes and the chromatin nucleolus are transversely 

 halved. The daughter chromosomes wander apart and before they 

 have reached the poles of the spindle become first elongated, and 

 then transversely constricted. The two centrosomes of each pair 

 diverge from one another, in a line perpendicular to the axis of the 

 original spindle, a tertiary central spindle (not formed from the 

 secondary one) appearing between them. By the separation of the 

 two centrosomes of a pair the mantle fibres become disassociated in 

 such a way, that in the dyaster stage only one fibre is attached to 

 each end of each chromosome. There is no trace of a rest stage 

 between this and the succeeding division, 



13) In the 2nd (and last) spermatocytic mitosis the 7 chromo- 

 somes and the chromatin nucleolus become arranged with their trans- 

 verse constrictions perpendicular to the axis of the spindle , so that 

 the 2nd division, like the first, results in a transverse division of each 

 of the chromosomes and of the chromatin nucleolus. In the succeeding 

 dyaster stage the chromosomes fuse and form a solid plate of 

 chromatin, around which a ring of idiozome substanze is grouped. 

 The bundle of connective fibres persists for a long time in the 

 cytoplasm. 



In conclusion, attention may be drawn to certain peculiarities in 

 the spermatogenesis of Penfafoma. 



There are 14 chromosomes in the spermatogonia. In the synapsis 

 of the 1st spermatocytes one of these becomes difiereutiated into the 



