The Spermatogenesis in Peutatoma up to the Formation of the Spermatid. 21 



The chromosomes soon lose their regular contours, and their 

 outlines become uneven. Concomitantly they increase in length and 

 in volume (Figs. 48—56). This increase in volume, at this early period 

 at least, is probably not an increase in mass, but is probably due to the 

 chromosomes acquiring a looser texture. The several chromosomes 

 do not grow to the same length and volume simultaneously. The elonga- 

 tion continues until some or all of the chromosomes have attained a 

 length of about the diameter of the nucleus (Fig. 57). Then they gradually 

 become grouped close together near the centre of the nucleus, the mass 

 separated by a broad zone of nuclear sap from the nuclear membrane 

 (Figs. 58—61). This process terminates in a stage (synapsis) where 

 the chromosomes are so densely grouped that the individual ones cannot 

 be distinguished (Figs. 62—70, PI. 2). 



The synapsis. 



This term was invented by Moore ('95) for a corresponding stage 

 in the spermatogenesis of Elasmobranchs. In Pentatoma the structural 

 relations of this stage seem to the same as in the cells described by 

 Moore, and in both cases (if not also in most cases of spermatogenesis 

 and ovogenesis) it is during this stage that the chromosomes undergo 

 the reduction in number. I agree with Moore that the central con- 

 densation of the chromatin at this stage does not represent an arte- 

 fact, since with fixation by Hermann's fluid, picro-acetic acid or cor- 

 rosive sublimate such cells are always found, alongside of cells in 

 other stages in which there is no such condensation of the chromatin. 

 The synapsis stage is very probably of general occurrence, and is 

 more frequently figured by the authors than described by them; thus 

 it occurs in Ascaris (Hertwig, and according to my own observations), 

 in Copepoda (Hacker and Rückert), I have found it in Harpalus and 

 Gryllus^ and according to Zimmermann it is a regular phenomenon in 

 plants. It would seem to be specially characteristic of the anaphases 

 of the 1st spermatocytes and ovocytes. 



In the synapsis (Figs. 62 — 70) the chromatin is densely massed, 

 so that the individual chromosomes cannot be counted; but the latter 

 nevertheless do not constitute a single mass, since projecting ends of 

 chromosomes may be seen. In describing the postsynapsis, we shall 

 have occasion to recur to the mode of fusion of the chromosomes 

 during the synapsis. 



To return to the chromatin nucleolus (w 2 of the figure). I give this 

 name in order to express its genetic origin, and to distinguish it from the 



