66 



account of their general character. The primitive testis-cells corre- 

 sponding to ovarian ova may be called spermatospores — whilst 

 the ovarian ova are termed oospores. — A fertilized ovum is an 

 oosp ermosp ore whilst an asexual spore is an autospore. In 

 Lumhricus and Hirudo (and in very many other forms belonging to 

 other groups of Invertebrata) the spermatospore by division of its nu- 

 cleus and incomplete fission of the protoplasm gives rise to a sperm- 

 polyplast or spermatosphere. Each constituent cell-element of 

 a sperm-polyplast is a spermatoblast or sperm-bud. By fission the 

 spermatoblasts multiply whilst remaining side by side, and ultimately 

 assume an elongated form — that of the ripe spermatozoon — the 

 elongated nucleus with a thin coating of protoplasm forming the head 

 whilst the vibratile tail is formed of the protoplasm only, which is extended 

 peripherally in the form of a filament. The most important fact with regard 

 to the type represented by Lumhricus is however this, viz. — that the 

 spermatoblasts do not take up all the protoplasm of the original sper- 

 matospore — but are arranged peripherally on a central mass of proto- 

 plasm which ultimately has the form of a large spherical corpuscle 

 many times larger in bulk than any one spermatoblast. This central 

 corpuscle I term the sperm-blastophor — or blastophoral 

 corpuscle, since it carries the spermatoblasts. 



The blastophor oi Lumhricus (and oi Hirudo and others) is de- 

 void of nucleus: it is also central in position . 



In Helix and Rajia I find the same elements present. The primi- 

 tive spermatospore gives rise by division of its nucleus to a number of 

 spermatoblasts which remain attached to a blastophor or corpuscle of 

 protoplasm corresponding to the sperm-blastophor of Lumhricus. In 

 Helix and Bana however — the blastophor possesses a large nu- 

 cleus and instead of being central — it is lateral in position, being in 

 fact adherent to the wall of the testicular follicle in which the develop- 

 ment of the spermatozoa takes place. 



The difi'erence in fhe two types of development together with the 

 fundamental identity of the blastophor or carrier of the spermatoblasts 

 is to be explained, as suggested to me by Professor Lank es ter, by 

 the fact that in Lumhricus the development of the spermatoblasts does 

 not occur in the testis itself — whilst it does do so in Helix and 

 Rema. In Lumhricus the spermatospores of the testis are continually 

 multiplying by fission in the base of the small testis and are thrown 

 off at its free surface whence they pass into the seminal reservoirs to 

 develop further. On the other hand the spermatospore of Helix and 

 Rana does not become detached from its seat of origin in the wall 

 of the testicular follicle. The development proceeds in situ. 



