The Spermatogenesis in Pentatoma up to the Formation of the Spermatid. 25 



structure is generally characteristic of spermatocytes. Thus Moore 

 ('95) found in Elasmobranchs about the beginning of the synapsis, 

 "a curious secondary nucleolus surrounded by a vacuole, which, so 

 far as I can ascertain, is in these fishes characteristic of this change". 

 The fact is, that so much of the study on spermatogenesis and 

 ovogenesis is carried on principally with regard to the relations of 

 the chromosomes, centrosomes and idiozomes, that the study of 

 nucleolar structures has been neglected. I am at present engaged on 

 a comparative study of chromatin nucleoli in various cells, whereby I 

 trust that it may be shown that under the term "nucleolus" are in- 

 clued at least three heterogeneous structures, namely the true nucleolus 

 (Montgomery, '98), the chromatin nucleolus, . and the karyosorae, the 

 name "nucleolus" having in most cases been applied to all these 

 structures promiscuously. Of particular importance would it be to 

 determine whether in cases, as that of Pentatoma just described, where 

 in the spermatogenesis a whole chromosome becomes thus meta- 

 morphosed, also in the ovogenesis similar process occurs ; and what 

 part such processes may play in the reduction of the chromatin. The 

 function of the chromatin nucleolus will be referred to later on. 



About the time of the synapsis the true nucleolus first appears, 

 one similar structurally and chemically to that of the spermatogonia; 

 the spermatogonic nucleolus disappeared in the prophase of mitosis. 

 In the synapsis the nucleolus arises as a small disc of finely granular 

 substance on the inner surface of the nuclear membrane {n Figs. 65, 

 66, 68, 73 — 75), the disc being convex on the surface directed 

 towards the nuclear cavity. The chromosomes are widely separated 

 from it at this time, so that it may be concluded that it is extra- 

 nuclear in origin, and at the time of first formation stands in no 

 relation to the chromatin (which is in accord with my previously ex- 

 pressed view, '98, in regard to the origin of the true nucleolar sub- 

 stance in general). Possibly this substance stands in some genetic con- 

 nection with the yolk substance {Y and Yh Gl, of the figures), which 

 appears simultaneously. As a rule the nucleolus remains in close contact 

 with the nuclear membrane during the synapsis, gradually increasing 

 in size, and then about the stage of postsynapsis departs from this position 

 (Figs. 76, 85), becomes more or less spherical, and then passes into 

 the nuclear cavity where it is always found in the rest stage (Figs. 95 

 — 100). Thus the true nucleolus passes from the periphery towards the 

 centre of the nucleus, the chromatin nucleolus in the reverse direction. 



Duiing the anaphase important changes occur in the cytoplasm. 



