32 SPERMATIC PARTICLES. 



In fishes, the lowest vertebrates, we find the structure of the testicle the most simple. 

 And even here, we perceive a grade as to their two grand divisions, marking diiferences 

 as wide as those of their other characters. In the Plagiostomes and Cyclostomes the 

 structure of the organ does not appear to have risen above the primitive cellular type, 

 that is, it is but a collection of parent cells, which have never advanced to the condition 

 of losing their identity as such by passing into seminal tubes. 



In the higher osseous fishes, a higher condition of things exists. There is an ad- 

 vancement beyond the cell-type, and the large cells appear to have passed either into 

 tubes or bundles of transverse folds, on the inner surfaces of which the parent sperm- 

 cells are produced, as before they were inside the large cells of those of a lower character. 

 The prolific nature of the testis, as a secreting organ, is just in proportion to these 

 convolutions and variations. And we find this prolificness in a ratio corresponding to 

 the liabilities of the semen reaching the ova of the females. Thus, in the lower orders, 

 the species of which are dormant and sluggish in their character, and which are almost 

 constantly in contact with the bottom of the water, the quantity of sperm to insure 

 the continuation of the species is necessarily less than in those higher and more active 

 orders, where, from their constant movement and travelling, the contact of the two may 

 be looked upon more in the light of an accident than otherwise. If, then, we are allowed 

 to reason on the relation of things, I think that in this fact may be found the reason of 

 the larger and more fertile character of the testes of the higher fishes. 



Among the Reptilia, Aves, and Mummaliu, with which the process of fecundation 

 takes place only by the conjunction of the sexes, a difterent and stricter economy is 

 manifested. The testes are more compact, their product less in quantity, and the value 

 of this quantity is shown by the means adopted for its contact with the ova by efferent 

 ducts, receptacles, and an intromittent organ. 



With these three grand classes, I need not refer to the difterences of size and ex- 

 ternal character everywhere met with ; they bear not at all upon the grand type of 

 testicular structure, but are referable to the economy of the species to which they be- 

 long. And only this much may be mentioned, that, generally speaking, as we approach 

 nearer and nearer the higher forms, the size of the testis compared with the whole 

 body is less and less, and the prolificness of the animal is less and less, because, per- 

 haps, the liabilities for the destruction of the species are in the minimum. 



We have now the organs for the elimination of the sperm. Our next inquiry is, 

 What are the preliminary steps of that process ? 



There is, in all the real glandular organs of the animal body, a common structure. 

 This is a layer or layers of epithelial cells, situated on a basement membrane, which last 



