GERM CELLS IX PEDICELLINA AMERICANA 37 



form, "the transverse marking separates two spermatogonia! 

 chromosomes which have conjugated end to end in synapsis." 



Of very considerable interest in this connection is the still 

 more recent work of Miss Stevens, '03, on the spermatogenesis 

 of Sagitta. This author, on good evidence, also decides for 

 synaptic-reduction. Thus: "Two types of spermatogonia! divi- 

 sions are found . . . ; one in which the daughter chromosomes 

 appear at the poles of the spindle as 18 rods . . . ; and another 

 type, where a much smaller number of loops, probably nine, 

 are found at each pole. . . . These figures lead me to think 

 that the so-called synapsis stage occurs in Sagitta at the close 

 of the final spermatogonia! division, the chromosomes uniting 

 in pairs at the poles of the spindle. There is so much variation 

 in the size of the spermatogonia, that it is impossible to be ab- 

 solutely certain that a resting stage where the chromosomes 

 are not visible does not intervene between this union of the 

 chromosomes" and the young spermatocytes "where usually 

 all the cells of a group contain nine distinct deeply staining loops 

 with a somewhat crenate or beaded outline." 



Evidence of a more general nature is that afforded, as Mont- 

 gomery again points out, in his latest review of the subject, '04, 

 by Ascaris megalocepJiala tmivalens, where only one chromosome 

 of large size occurs in the young spermatocyte in place of the 

 two present in the last spermatogonia! division. Also, in those 

 cases where two chromatin nucleoli (accessory chromosomes, 

 McClung) appear in the spermatogonia and oogonia (Afiasa) 

 only one of these bodies appears after the synapsis, and this is 

 then of a double character. At no point during this period is 

 there even a suggestion of the tlirowing out of chromatin from 

 the nucleus. It then seems evident in these cases, tliat the re- 

 duction is accomplished by tlie conjugation of the single indi- 

 viduals. 



Still later is the preliminary report of A. & K. E. Schreiner, 

 '04, on the Spermatogenesis in the Vertebrates, Myxine glutinosa 

 and Spinax niger, where immediately following the last sper- 

 matogonia! division the chromosomes, in the form of extended 

 thin threads group at one pole of the reformed nucleus and 



