XII.] CONJUGATION AND SEXUAL REPRODUCTION. 149 



towards the ends, so that at last only the two points are left 

 free. Of course all this can only be tested by the preparations 

 themselves, and O. Hertwig is in the best position, from the 

 great number of his sections, to decide whether his interpre- 

 tation or that which I have offered, is the right one. 



Should my surmise be confirmed, it follows that even in so 

 small a number of idants as exist in the variety univalens, 

 a number of combinations would be possible, inasmuch as 

 halving the rods doubles the number of units capable of com- 

 bination, and, of course, any two half rods might fuse in the 

 manner described above. 



It would be very easy to explain the fresh combinations of 

 germ-plasm in all species, Ascaris m. imivalens included, if we 

 might assume that the idants were freshly built up of irregularly 

 distributed ids after each resting-stage of the nucleus. But the 

 above-mentioned facts concerning hereditary transmission from 

 one parent alone, which have already been used as evidence, 

 are opposed to this view. 



It is self-evident that I am far from claiming to have found 

 the correct interpretation of the details in every case. When 

 other workers have tested anew the processes with which my 

 attempted explanation deals, and when new facts have been 

 discovered, we shall gradually arrive at greater certainty. 

 I chiefly look for progress from the comparative investi- 

 gation of corresponding processes in many different groups of 

 animals. For the present we may well rest satisfied, if at any 

 rate the meaning and significance of the two nuclear divisions 

 are, upon the whole, recognized as true. 



The future will teach us whether this is the case. In the 

 meantime it promises well that, under the guidance of this 

 thought, the apparently irreconcilable processes in Ascaris and 

 Pyrrhocoris can be brought together under a common point of 

 view. From this standpoint the two divisions of the germ- 

 mother-cell signify a period of reduction and of reconstruction of 

 the idioplasm. If reduction alone were needed— i. e. a dimmution 

 of the number of ids by half — a single division would have suf- 

 ficed ; but the second was rendered necessary in order to 

 attain the greatest possible diversity in the germ-plasm. The 

 accomplishment of these two ends is not always brought about 

 by precisely the same course, but nature pursues somewhat 



