42 DUBLIN 



point of development. Altogether the evidence points to the 

 conclusion that the continuous spiremes and ophiuroid figures 

 are alike in nature and represent, in somewhat different detail, 

 the same process, viz., the secondary union of the ends of the 

 already formed bivalents. In the first case the apposition is 

 continuous, one bivalent being attached to the free end of the 

 preceding ; in the second, the ends of several bivalents are 

 united at the same point. The difficulty has arisen, I believe, 

 because Hacker has sought the process of reduction in the 

 period of oocytic growth when, as a matter of fact, it occurs at 

 a very much earlier period in the early telophase of the last 

 oogonial and spermatogonia! divisions, where, through a proc- 

 ess of convergence and fusion of univalent elements into pairs, 

 the number is halved. 



Once formed, the bivalents may persist individually as is so 

 clearly shown in Pedicelliiia, both in the o^gg and in the sperm, 

 or they may fuse into one deeply staining mass, emerging only 

 later in their true form as in Peripatiis. The Cope pods are ap- 

 parently of the same type. The characteristic " synapsis-stage " 

 occurs, as Hacker himself asserts, and is clearly coincident with 

 the last oogonial telophase. Following this synapsis stage, 

 when the growth period sets in, the already formed bivalents 

 apparently increase in size, lose in staining capacity, and cross 

 and recross, giving rise to the confusing figure which Riickert 

 describes (cf. his Fig. 3, PL XXI), and from which, with the 

 growth of the nucleus, the parallel rods emerge. Before this 

 clearing-up process, however, when the chromosomes are still 

 much crowded, they may unite end to end in a long chain to 

 form the continuous spireme of which Hacker speaks. The con- 

 ditions in the spermatogenesis of the Amphibia present an inter- 

 esting corollary to the above discussion. Flemming, ''^J ^ and a 

 number of others have described a continuous spireme in the 

 spermatocytes which segments, as in the Copepods^ into the re- 

 duced number of bivalents. Montgomery has, however, in a 

 very recent work, been unable to find the continuous spireme 

 and describes a type of reduction quite similar to that he ob- 

 served in Peripatiis. To this conclusion we shall return pres- 

 en 



