Papers from the Marine Biological Laboratory at Tortugas. 201 



claimed, the lower Prosobranchs should show this peculiarity, which they 

 do not. He comes to the conclusion, then, that they are functionless. 



Now Meves has shown that the oligopyrene spermatozoa of Paludina 

 in their development show a marked parallelism — not to the ova, but 

 to the true spermatozoa, and that they are produced in numbers equal to 

 the latter. He suggests that there may be certain conditions under which 

 they do fertilize the eggs; granting that they do and since the nucleus is 

 accepted to be the bearer of heredity, then an embryo resulting from an 

 egg fertilized by an oligopyrene or apyrene spermatozoon would show pre- 

 ponderating female characteristics. Such a case would prove the hypothesis 

 that the nucleus is the bearer of heredity. The spermatozoon would then 

 have, either primarily or solely, the mere function of stimulating the egg to 

 division. According to Boveri, this stimulus is due to the introduction of a 

 centrosome into the egg. But if it should be shown that actually the oli- 

 gopyrene spermatozoa never fertilize the egg, then Meves would take the 

 view, with Brock, that they are functionless. 



Stephan ('03a) investigated the apyrene spermatozoa of Cerithium vul- 

 gatiini, Murex trunculus, M. brandaris, Triton nodifer, and Nassa mutabilis. 

 All of these forms he reported to have apyrene spermatozoa whose devel- 

 opment is comparable to that of the oligopyrene of Paludina. All of the 

 chromatin disappears in the atypical spermatozoa of these forms and in 

 every case except Cerithium the bundle of axial fibers never comes into 

 contact with an existing nucleus, as is the case in Paludina. In Cerithium 

 the advancing bundle of axial fibers does touch a small nucleus which is 

 the equivalent of a chromosome. Before the fibers have completed their 

 growth, however, this small nucleus degenerates and disappears completely. 

 Again, in Cerithium, as in Paludina, the cilia persist, while in the other 

 forms they are retracted before the spermatozoon has fully matured. 

 Upon these facts and also upon the positions of the anterior centrosomal 

 structure in the adult atypical spermatozoa of the different forms under 

 investigation, he concludes that gradations may be established between 

 the different types of atypical spermatozoa, with Cerithium occupying an 

 intermediary position between Paludina and the others. 



In another paper Stephan ('036) described briefly the development of 

 the apyrene spermatozoa of Murex brandaris. The development here agrees 

 in general with the description given by Meves for the oligopyrene sper- 

 matozoa of Paludina. It differs in the facts that there is an intense vacu- 

 olization of the cytoplasm and that there is no nuclear element in the adult 

 spermatozoon.^ 



Basing his conclusions on certain observations of Popoff which were 

 published later, R. Hertwig ('05) expressed his belief that the oligopyrene 

 and apyrene spermatozoa serve to fertilize the egg, but such fertilization 

 would not be a uniting of the male and female nuclear components, and 

 would stand on the boundary between parthenogenesis and true fertilization. 



' A third paper by Stephan ('03c) on the development of the apyrene spermatozoa of Cerithium vulgalum 

 and Nassa mutabilis, with two figures, was Inaccessible to me. 



