HERMAPHRODITISM IN NEMAS 209 



common in this genus, and that similar spermatozoa are present in a number of 

 other species, but thus far I have no proof that in these other species the sperma- 

 tozoa are functional. These results lend additional emphasis to my suggestion, 

 made in previous papers, that parthenogenetic species in general be reexamined 

 with a view to ascertaining whether some of them do not present spermatozoa 

 of minute size. As in the present case, species hitherto regarded as partheno- 

 genetic may prove to be syngonic. Probably thousands of nemas are syngonic. 



Hermaphroditism in Nemas. Dr. E. Maupas in 1900 summarized to that date 

 a list of 34 hermaphroditic species belonging to 12 different genera, as follows: 

 Rhabditis, Diplogasier, Cephalobus, Plectus, Allantonema, Bradynema, Micro- 

 laimus, Angiostomum, Strongyloides, Dorylaimus, Aphelenchus, and Alaimus: 

 four of them parasitic, the remainder free-living. These 34 species represent 

 varying degrees of hermaphroditism, from species with two sexes, both func- 

 tional, but presenting also females capable of developing their own spermatozoa, 

 to those in which only female forms are known, but in the gonads of which first 

 spermatozoa then ova are produced, the spermatozoa serving to fertilize ova 

 from the same gonad. Of these 34 species, over half belong to Rhabditis. 



Syngonic Forms.* I have recently taken occasion to look somewhat carefully 

 into the embryology of a number of species, all of which prove to be syngones 

 or digones. These are the filter-bed species Mononchus longicaudatus Cobb, 

 Ironus ignavus Bastian, Ironus longicaudatus de Man, Plectus cirralus Bastian 

 and Tripyla monohystera de Man, all species that have been repeatedly investi- 

 gated by different observers in various parts of the world. To three of them 

 males are unknown; in the case of the fourth, Ironus ignavus, the males have been 

 seen but rarely. In addition I have examined an interesting new genus, Monon- 

 chulus, also hermaphroditic. In the course of my investigations extensive 

 series of individuals have been examined, in nearly every case several hundred, 

 all of which proved to be syngonic females (digonic in Mononchulus). As in 

 most of the other hermaphroditic nemas, the spermatozoa are produced in the 

 young gonad and are early sent forward,' often to a special receptacle, where 

 they await the arrival of the ova. 



Potency of Syngonic Sperm. In the light of recent researches on the fertili- 

 zation of the ovum several interesting questions again arise in connection with 

 the origin, development and function of these spermatozoa produced by gones 

 which simultaneously or subsequently produce ova. Are these spermatozoa 

 functional? That is to say, do they fertilize the ova in the "regular" manner? 

 Do the syngonic spermatozoa enter the egg and behave in every respect like those 

 produced in a separate male organism, or do they behave in some other way? 

 To answer these questions, among other things the history of the chromosomes 

 throughout the ripening of both sperm and ova should be accurately known, 

 and then compared with the corresponding facts in typical amphigonic species. 



]'(in.ishing Series of Spermatozoa. Mainly, previous researches have given 

 us the records of species in which the spermatozoa produced by syngonic females 

 were of the same size and form as those produced by the few males that a so 

 occurred, that is to say relatively of very considerable size. In some species the 

 males of which are unknown, the recorded spermatozoa, found in the female, 

 are relatively small and difficult ^o observe. My own researches have led me 

 to cases more and more difficult to decipher, owing to the smaller and smaller 

 size of the spermatozoa discovered, and ended in cases in which I was left com- 

 pletely in doubt as to the existence of spermatozoa; I could find none, but the 

 nature of my experience did not permit me to conclude that therefore none 



For the terminology used in the following discussion, see pp. 126, 127. 



