210 FILTER-BED NEMAS 



existed. Sometimes the spermatozoa are so small, and so difficult to observe, 

 even under the best of conditions and with the best instruments used by ex- 

 perienced observers, as to lead me to begin to question the adequacy of the evi- 

 dence upon which we base our belief in some cases of alleged parthenogenesis. 

 May it not be that sperm cells, small and difficult to observe, have escaped notice? 



Potency. As to the efficacy of these small spermatozoa, in all the cases I 

 have observed there seems to be a fair volume of evidence that the eggs are fer- 

 tilized by the entrance of a body so closely resembling one of these small sperma- 

 tozoa as to leave either no or little doubt that, so far, the phenomena are identical 

 with those of bisexual fertilization. Spindles and polar bodies are formed, though 

 sometimes the evidence is not complete. Unfortunately, in most of the cases I 

 have observed, the chromosomes are so small and crowded as thus far to preclude 

 exact counting; I am therefore unable to say, on the basis of fully satisfactory 

 observations, that fertilization always takes place in the same manner as in the 

 case of females fertilized by copulation with males. I can only say that my 

 evidence, as far as it goes, points that way in a considerable number of species. 



In view of the present developments this would seem to be a matter in which 

 it is well to keep clearly in mind that no amount of not seeing a thing proves that 

 it does not exist. It is no longer the case, as it formerly was, that non-existence 

 of males may be regarded as proof of parthenogenesis. We must prove that 

 there are no functional spermatozoa produced by the females themselves. Has 

 this always been done? I think the answer must be "No," or "Not satisfactorily." 



Road to Parthenogenesis? With Maupas one may suspect syngonic nemas to 

 be on the road to parthenogenesis. This suspicion may be justified on the 

 ground that we find species producing two groups of sexual cells, one male, the 

 other female, variously arranged with respect to each other all the way from 

 amphigony to the most intimate syngony, a series at once suggesting the hypoth- 

 esis that bisexual nemas may be evolving along this road to parthenogenesis. 

 What would be the ulterior (post-parthenogenetic) steps in such an evolution? 



Consider for a moment the origin of the gonic cells in a syngonic nema: At 

 some time in the growth of its gone all the future ova and spermatozoa exist 

 in the form of a single or primary gonic cell, destined to give rise both to sper- 

 matocytes and oocy tes. The spermatocy tes usually take the lead in development 

 and give rise to spermatozoa that are lodged in the uterus. In some cases almost 

 simultaneously, in others only a few hours later, the oocytes begin to develop, 

 and give rise to ova, which in turn pass onward to be fertilized by the sperma- 

 tozoa already produced by the same gone. Admitting the crudeness of the 

 questions, Is not this conceivably a wasteful method? Under the circum- 

 stances might it not be more "economical" to produce only one kind of cell, 

 each such cell to contain both male and female elements? Why separate these 

 complements only to bring them together again so soon? These queries are of 

 course merely suggestive, and are not meant to outline the whole subject. 



The original gonic cell of a syngone gives rise to both spermatozoa and ova; 

 hence there exist in it, among other things, both male and female potentialities: 

 these must have some physical embodiment, of course not necessarily dis- 

 cernable. Should these potentialities, male and female,* be separately embodied 

 in the original gonic cell in numbers suitable* each to each, why might they not 

 there and then, in ways harmonious with those familiar in amphigony, segre- 

 gate their parts and regroup them, and afterward develop in the form of some 

 fractional number of syncysts? Is this anything more than following to what 

 would appear to be a logical conclusion, the tendencies apparently existing in 



* "Potentialities, male and female", being, of course, merely members of a series of potentialities 

 subject to heredity. 



