Reproductive Processes of Sponges. 383 



p. 128). Then the time varies with the species, as Grant 

 has observed (no. 1, p. 133). 



The spermatozoa which I saw in 1854 bore the proportion 

 of about 1 to 5 when compared with the average size of the 

 common sponge-cell in Spo7igilla, as the latter is much the 

 largest. Those which Lieberkiihn figured in 1856 bear a 

 similar ratio ; and so do those figured by Schulze in Hali- 

 sarca lobularis. 



The smallest size at which I could recognize the egg in 

 Halisarca lobularis was l-3000th inch (no. 13, p. 31, pi. xx. 

 fig. 3, a) ; while the monociliated sponge-cell of the ampulla- 

 ceous sac was a little smaller, viz. about l-3600th inch in dia- 

 meter {ib. fig. 2, a) ; and Schulze's figures of the body of a 

 monociliated collar-cell (" Kragenzell"), compared with that of 

 the spermatozoid (no. 17, I. c), give about l-18000th of an 

 inch for the latter. It might be thought that it would have 

 been better to have been able to omit the indefinite word 

 " about " {circa) ; but those who have studied the minute ana- 

 tomy of sponges well know that all their soft parts afford, 

 from polymorphism and actual difference in size, only ap- 

 proximate measurement. 



Hackel is the only one who believes (" glaube ") that he has 

 seen the spermatozoids enter the ovum (no. 11, vol. i. p. 396, 

 Atlas, Taf. 48. fig. 6) in Sycortis lingua=Grantia ciliata, 

 Bowerbank. 



Keller of Zurich also gives a figure of it in Leucandra 

 aspera, H., with reasons for coming to the conclusion (no. 16, 

 p. 21, Taf. 1. fig. 4,c). 



But of all those who have so deeply studied the living 

 calcareous sponges, it has been reserved for Hackel alone to 

 see the act] and this, according to his statement (no. 11, vol. i. 

 p. 396), he has done repeatedly (" wiederholten Malen "). Yet 

 if his statements and figure are like those which he has given 

 of my Squamulina scopula (' Jenaische Zeitschrift f. Natur- 

 wissen.' Bd. ix. 1877), I regret to be obliged to say that they 

 are not trustworthy, as may be seen by Saville Kent's ample 

 confirmation of my observations of 1870 in lb78 (Ann. 

 vol. ii. p. 68, pis. iv. & v.) ; while it was not difficult to con- 

 jecture, with apparent certainty, that which the sagacious 

 Lieberkiihn had indicated sixteen years before by his descrip- 

 tions and figures of the swarm-spore and spermatozoa respec- 

 tively in SpongiUa (I. c). 



Another difficulty here presents itself, viz. that, from the 

 polymorphic condition of all the soft parts in the living 

 sponge, even to the capsule of the ovum, it becomes doubtful, 

 unless the spermatozoon is seen to enter the ovum, whether 



