Elements of the Spongida. 355 



within the ^' spermatoa''^ (the former in Halisarca lohularis in 

 1877, and the latter in Sycandra rcq)hanus in 1883), I cannot, 

 in my spirit-preserved specimens of ovigerous sponges (some 

 of which were taken off the rocks at this place), where they 

 appear to be present, be satisfied that they are so ; nor do I 

 think, without seeing them in their living state in motion^ it 

 would be possible almost under any circumstances in their 

 separate state, that is out of tlie " spermatoa," to find them ; 

 for even when two or three only are left within the sperma- 

 toon, a microscopic power, according to PolejaefF, of from 800 

 to 1500 diameters is required for this purpose. 



In both Schulze^s and Polejaeff's preparations, which con- 

 sist of microscopic slices stained and mounted on glass 

 slides, the spermatozoa are evident where all together in 

 the " spermatoa ; " but the " spermatoa " not only vary in 

 size in different species, but also in the same specimen, while 

 the form of ihe head of the spermatozoon also differs — cir- 

 cumstances to which I have already alluded, in order that the 

 student should not expect everything to be exactly alike in 

 every instance. 



Thus in Halisarca lohularis the " spermatoa " on Prof. 

 Schulze's slide vary under 15-6000ths inch in diameter, 

 while on Dr. Polejaeff's (viz. in Sycandra raphanus) they do 

 not exceed 5-6000ths. 



Again, the head of the spermatozoon in Spongilla,ixs represen- 

 ted by Lieberktihn, is oval, acuminated backwards or towards 

 the tail. That of Sycortis quadrangidata {Grantia ciliata, 

 Bk.), according to HackeL, is elliptical, acuminated at each end 

 (' iJie Kalkschwiimme,' Atlas, Taf. xlviii. fig. 7). Those 

 which I saw in July 1870 in Microciona atrosanguinea^ Bk., 

 under a power of from 3 to 600 diameters (described in the 

 * Annals,' vol. vi. p. 339, but not figured until 1874, vol. xiv. 

 pi. X. figs. 17-20), were flask-shaped, with the acuminated end 

 anteriorly, very like those represented by Eimer in 1872 ] 

 while two of those delineated by Schulze in Halisarca lohu- 

 laris have hammer-shaped heads — that is, the head is ovoid, 

 but applied to the tail transversely; and in PolejaefTs 

 <lelineatious from Sycandra raphanus they are spherical. 



How far the shape of the head of the spermatozoon may 

 be polymorphic, and therefore vary in form according to cir- 

 •cumstances, even in the same species or specimen, I am unable 

 to say, so would not lay much stress on these differences ; 

 while, whatever the shape may be, each appears to be furnished 

 with a single light-refracting globule or nucleus. 



As the spermatozoa are developed in a nucleated cell, viz. 

 -the " sperniatoon," they may sometimes be in a preliminary 



