734 JOHN BEARD, 



consulted. Apart from minute details concerning certain aspects of 

 spermatogenesis — which do not concern us here — it contains brief 

 references to the history and morphology of the two sorts of spermato- 

 zoa in Paludina, and also in one of the Lepidoptera, Fygaera 

 hucephala^ in which Meves has likewise found two kinds of spermato- 

 zoa to be present. His promised memoir on these forms will be 

 looked forward to with much interest, especially after his statement, 

 that, unlike previous observers, and in particular M. von Brunn, he 

 finds a complete parallelism in the development of the two kinds. 



According to this observer, the order of the generations of cells, 

 which precede the spermatids, or forerunners of both kinds of sper- 

 matozoa, has hitherto been wrongly described. As in other animals, 

 one can divide the development of the spermatozoa in Paludina 

 into the three well-known periods. These are, one of increase in 

 number, one of growth, and one of ripening. The first period, 

 in which the spermatogonia or primitive sperm -cells increase 

 by repeated divisions, is common to the ancestral cells of both sorts 

 of spermatozoa in Paludina. The development diverges, when these 

 divisions have ceased, on the entry into the period of growth. Here 

 the one set of cells attains a less size than the other. In both sets 

 of cells the usual two divisions take place in the ripening period, 

 and of the spermatocytes, which enter this period, the smaller give 

 rise to the hairlike or ordinary form of spermatozoa, the larger ones 

 to the wormlike (Fig. B). 



I have quoted his interesting account at length, because it appears 

 to be clear from it, that the separation into direct forerunners of 

 unlike gametes here takes place at the latest in the final division of 

 the spermatogonia, where these pass into the growing period, and 

 become spermatocytes. The result is not effected by the consideration, 

 that the wormlike spermatozoa are non-functional. There are here 

 two sorts of gametes — as in the female skate — and their direct 

 forerunners would appear, from Meves' observations, to be differen- 

 tiated exactly at the point previously suggested for those of the two 

 sorts of eggs ^). From his brief reference to the two kinds of spermato- 



1) It is commonly believed, that the number of divisions of the 

 germ-cells to their "maturations"' is always very many. A little con- 

 sideration will show the absurdity of this assumption. In the devel- 

 opment of a female-egg in P. batis the primitive germ-cell divides 

 nine times, yielding 512 primary germ-cells. Seven further divisions 

 of 512 cells would result in 65536. (In a child's ovary Allen Thom- 



