THE SPERMATOZOON. 67 



In most Hydrozoa the subepithelial epiblastic cells become 

 converted into germinal cells (spermospores), and then break up 

 to form spermoblasts, each of which becomes a spermatozoon. 



In most higher Metazoa the spermospores usually form the 

 epithelium of an ampulla or tube, though more rarely (many 

 Chaetopoda, Gephyrea, etc.) they may be derived from cells lining 

 the body-cavity, as in the case of ova. The spermatozoa are 

 formed either by the direct division of the spermospores into a 

 number of cells, spermoblasts, each of which grows into a sper- 

 matozoon ; or by the nucleus of the spermospore becoming 

 subdivided within the cell body, the latter differentiating itself 

 into the tails of the spermatozoa while the segments of the 

 nucleus give rise to the main part of the heads. 



In many instances interstitial cells which do not give rise to spermatozoa, 

 are intermingled with the spermospores. 



In a good many cases, as first pointed out by Blomfield 1 , the whole of 

 each spermospore does not become converted into spermatozoa, but part, 

 either with or without a segment of the original nucleus, remains passive, 

 and carrying as it does the off-budded spermoblasts may be called the 

 * sperm-blastophor.' This passive portion of protoplasm is not employed 

 in the regeneration of the spermoblast. This very singular phenomenon 

 has been observed in Elasmobranchii, the Frog, the Earthworm, Helix, etc. 2 , 

 and probably has a much wider extension. In Elasmobranchii (Semper) 

 the passive portions of protoplasm are nucleated, and are placed on the 

 outer side of the columnar spermospores which line the testicular ampullae ; 

 they are not distinctly differentiated till the nuclei, segmented from the 

 nucleus of the primitive spermospore to form the heads of the spermatozoa, 

 have become fairly numerous. In the Frog the passive blastophor also 

 occurs as a nucleated mass of protoplasm on the outer side of the spermo- 

 spore. In the Earthworm the blastophor forms a central non-nucleated 

 portion of the spermospore ; and the whole periphery of each spermospore 

 becomes converted into spermoblasts. 



It has been already stated in the introduction that the male 

 and female generative products are homodynamous, but the 

 consideration of the development of the products in the two 

 sexes shews that a single spermatozoon is not equivalent to an 

 ovum, but rather that the whole of the spermatozoa derived from 

 a spermospore are together equivalent to one ovum. 



1 Quart. Journ. of Micro. Science, Vol. XX. 1880. 



2 Blomfield, loc. cit., p. 83, states that he has observed this fact in Lumbricus, 

 Tubifer, Hirudo, Helix, Arion, Paludina, Rana, Salamandra, and Mus. 



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