Mr. H. J. Carter on the Reproduction of Sponges. 425 



ones — measurements which at all times, of course, with such 

 small objects, of such a polymorphic nature, and viewed under 

 such circumstances, should only be regarded as approximative. 



I have already stated (Annals, I. c.) that, among the marine 

 siliceous sponges, Halichondna simulans, from its hardiness 

 and the apparently larger size of its sponge-animalcules, to- 

 getlier with its plentifulness, affords one of the best species for 

 observations of this kind. 



Besides the figure of zygosis above described and given in 

 the plate, there are others where the sponge-animalcules are 

 united linearly, like the individual Diatome^ in the filament 

 of Melosira, with here and there a conjugation like that of our 

 illustration. Schmidt has also figured something of this kind 

 in an allied species, viz. Reniera aqueductus (Adriat. Spong. 

 1st Supp. pi. 1. fig. 12). But, with the polymorphic nature of 

 the sponge-animalcule, such diversities of form being unlimited, 

 our present object has been to select that which is most like 

 zygosis in every respect, an almost facsimile of which I figured 

 long ago in Amoeba radiosa (?) (Annals, 1856, vol. xviii. pi. 5. 

 fig. 17). 



Not knowing until last year the form of the sponge-animal- 

 cule by actual observation, I only viewed this conjugation as 

 very like zygosis in the Dijjiugioi ; but now that I am familiar 

 with the figure and habits of this animalcule, the identity of 

 the process seems to me complete. 



Thus having obtained a starting-point for our history of the 

 reproductive process of the Spongiadaj by impregnation, let 

 us revert to the seed-like bodies in the Tethyce^ for the pur- 

 pose of following it up to the fully developed young animal of 

 the Shetland species, with which we are now most immediately 

 concerned. 



And taking a portion of the sarcode of T. zetlandica (i. e. 

 from fig. 13), it will be found, when torn to pieces in water 

 under tlie microscope, to be thickly charged with granuliferous 

 cells about 15-6000ths or 1 -400th of an inch in diameter 

 (fig. 7). There is, of course, a wide difference between this 

 size and even that of the body of the sponge-animalcule, which 

 may be set down roughly about the 3000th of an inch. But I 

 can recognize with certainty in these spirit-preserved specimens 

 no stages between the two sizes ; so I must be content to as- 

 sume tliat this is an advanced state of the sponge-ovule, what- 

 ever its original size might have been. 



When further examined, this cell is observed to be filled 

 with nucleated cellules (c) , each of which is again filled with 

 minute granules [d) , and in the midst of all an efiete (?) nuclear 

 cell (6), like that seen in \\\t Dlfftuqice and Amaeha' (see also 



Ann. d; Mag. K Hist. Ser. 4. " Vol. ix. 29 



