THE BEGINNINGS OF LIFE. 213 



to the male reproductive elements, both in Animals and 

 in Plants, we shall find them invariably arising out of 

 modifications taking place in the protoplasmic contents 

 of certain cells or vesicles. Thus Wagner and Leuckart, 

 after pointing out that spermatozoa in the various kinds 

 of animals are produced separately in the interior of 

 vesicular elements, as was first made known to us by 

 Kolliker, say 1 : c It is difficult to trace the intimate 

 development of the spermatozoa in the interior of these 

 vesicles ; but It appears probable that if is brought about 

 by the junction of molecular corpuscles, which join each 

 other linearly, and which have been deposited from 

 the contents of the vesicles.' With regard to the 

 precise nature of the c vesicles' of development, 

 however, there is some uncertainty. In very many 

 cases they are undoubtedly, as Kolliker supposed, 

 nuclei; and referring to this view Wagner and Leuc- 

 kart say : c The unity in the mode of development of 

 the spermatozoa which would thus be established is 

 certainly very attractive; but we dare not conceal it 

 from ourselves that this inference from analogy is the 

 less to be depended upon, since the genesis of the 

 spermatozoa in the Decapoda furnishes us with a proof 

 that the formation of these elements may also take 

 place immediately in the interior of cells, without 

 the nuclei at all participating in it.' All the known 

 modes of origin of these spermatic bodies may, however, 



1 Art. ' Semen,' ' Cyclop, of Anat. and Physiol.' vol. iv. p. 499. 



