738 JOHN BEARD, 



come into play at some period or other of the developmental history. This 

 is quite what might have been expected, for, as already noted, no 

 single case of two sorts of functional spermatozoa is known. 



In Paludina vivipara, from the statements of M. v. Brunn and 

 Meves, the wormlike spermatozoa appear to be as numerous as the 

 ordinary form. Other instances only approach without reaching this 

 full development; indeed, from the literature it would not be difficult 

 to put together a list of cases, showing all sorts of retrogressive 

 stages from those, like Bombinator (Ivar Broman) with fully 

 formed "giant-spermatozoa" and spermatocytes in degeneration, to 

 others with little or nothing else to represent the second form of 

 spermatozoon except degenerate spermatogonia. 



In some cases this faculty has been retained by the male. This 

 retention of a second form of male gamete, interesting and significant 

 though it be to the embryologist, to all appearance has no functional 

 import. It serves, however to indicate, that the conditions were 

 originally alike in the two sexes ; and in this way its existence removes 

 difficulties in the way of a true and proper appreciation of the facts 

 in the female. The circumstance, that in some instances, at any rate, 

 the male also possesses the faculty of differentiating two sorts of 

 gametes, throws another light on the production of two kinds of eggs 

 by the female. This loses much of its apparently teleological 

 character. 



But it is the egg, which invariably develops, and not the sperm- 

 atozoon. In all animal development an egg is essential, though on 

 occasion a spermatozoon may be dispensed with. The function of 

 the latter is thus reduced to the bringing about of the effects due to 

 amphimixis, and for this reason the development of a second kind of 

 spermatozoon is unnecessary. 



Since the above was written the two following papers have appeared : 

 Nils Holmgren, Ueber den Bau der Hoden und die Spermatogenese 

 von Staphylinus (a Coleopterous insect, allied to the dung-beetles), 

 in: Anat. Anz., V. 19, No. 18, 27th June, 1901, p. 449—471, 5 figs. In 

 this paper the author records for this insect two sorts of spermato- 

 gonia and two categories of spermatozoa. — F. Meves, Ueber die 

 sog. wurmförmigen Samenfäden von Paludina und über ihre Ent- 

 wicklung (vorgetragen im physiologischen Verein in Kiel am 20. Mai 

 1901), Separat- Abdruck aus "Mittheil. f. d. Verein Schlesw.-Holst. 



