230 Papers from the Marine Biological Laboratory at Tortitgas. 



and Paludina and indeed of other forms in which they have been described. 

 The first of these is the relatively immense growth of the cell which ulti- 

 mately gives rise to the atypical spermatozoon. Second, the history of 

 the centrosome and the development of the axial fibers of the atypical 

 spermatozoon present close parallels in Strombus and Paludina. The 

 centrosome fragments and gives rise to a number of centrioles; the division 

 of these with the subsequent separation of the daughter centrioles results 

 in the formation of the bundle of axial fibers. In Strombus the differenti- 

 ation is carried further, in that the bundle of axial fibers splits and the two 

 halves move laterally to the surface of the cell and there form the two undu- 

 lating membranes. Very similar phenomena have been described by 

 Stephan ('036) and by Lams ('09) for Murex and by Kuschakewitsch ('11 

 and '13) for Vermetus. In fact, in every form in which the developm.ent of 

 the atypical spermatozoa has been described we find the differentiation of 

 the centrosomal element into axial fibers. 



Perhaps the most generally constant phenomenon in the development 

 of the atypical spermatozoa of different forms is the fate of the chromatin. 

 In Paludina, according to Meves ('03), one chromosome is retained and 

 forms the nucleus of the adult oligopyrene spermatozoon, while all the rest 

 of the chromatin degenerates. A similar condition is held by Lams ('09) 

 to be the case in Murex, although Stephan ('03&) had previously reported 

 that in this form all of the chromatin degenerates. In all other forms in 

 which the matter has been investigated, the nucleus breaks down and an 

 atypical spermatozoon is developed which contains no chromatin. Another 

 characteristic held in common by the atypical spermatozoa of certain forms 

 is the fact that the products of metabolism are stored in the cell. Thus, 

 we find large secreted bodies in the atypical spermatozoa of Strombus, 

 Pteroceras (Brock, '87), and Vermetus (Kuschakewitsch, '11 and '13). It is 

 probable, too, that the mitochondrial apparatus, so beautifully described 

 and figured by Retzius ('05), in the oligopyrene spermatozoa of Paludina 

 is of the same nature, as well as the refractive bodies described in the 

 atypical spermatozoa of Cyprcea by Brock ('87), of Murex by Koehler ('88), 

 and other writers and the vacuoles in the apyrene spermatozoa of Conus 

 described by Schiemenz ('96) and Kuschakewitsch ('11 and '13). 



Both Stephan ('03a) and Kuschakewitsch ('11) have suggested the 

 possibility of arranging the atypical spermatozoa of different forms into a 

 gradated series based upon differences in their development and structure 

 and representing further and further retrogressions from the typical sper- 

 matozoa. At the head of such a list would be placed Paludina and Murex 

 in the order named. Next would come Conus, for here Kuschakewitsch 

 ('13) has recently found that one division normally occurs in the develop- 

 ment of the apyrene spermatozoon. After these there might follow in 

 succession Cerithium, Vermetus, and Strombus. The list can not safely be 

 extended further than this, since we are not sufficiently acquainted with the 

 phenomena which take place in other forms; and even as it stands the list 



