212 B YRNES. [Vol. XVI. 



methods of staining, the spermatozoon shows always a precisely 

 similar structure. 



In the last stage of the formation of the spermatozoon of 

 Limax agrestis the sperm-head appears heart-shaped in optical 

 section. The tail of the spermatozoon is very long and slender, 

 as is usual among the mollusca. The tail becomes somewhat 

 thickened near the head and passes into the head as an axial 

 rod. In cross-section the axial rod is seen to be surrounded by 

 a mass of chromatin in the shape of a trefoil. The maturation 

 of the spermatozoon seems to be completed by the spiral twist- 

 ing of the sperm-head ; the proximal part of the tail is also 

 involved in the formation of the spiral, as shown in PI. XII, 

 Fig. 40. In the mature spermatozoon the chromatin appears 

 as a delicate though deeply staining cord, twisted spirally round 

 a refractive, colorless axis. I have not been able to differentiate 

 a middle-piece in the spermatozoon. When the mature sper- 

 matozoa are taken from the ducts of the ovo-testis and mounted 

 on a slide, the slender distal part of the tail often wraps itself 

 around the proximal part as a whip around the handle. 



2. Fertilization. 



The youngest fertilized ova that could be found in Limax 

 were those stored in the lower part of the oviduct. I have 

 succeeded in finding but very few ova at this stage. It is 

 impossible to determine how long the sperm-head has been in 

 the eggs that are taken from the oviduct, for the eggs of Limax 

 are not laid immediately after copulation. I have dissected 

 individuals immediately after copulation and have found no ova 

 in the oviduct. Moreover, a careful watch has been kept over 

 slugs that have been seen copulating, but they laid no eggs 

 within the following twenty-four hours. The spermatozoa are, 

 therefore, probably stored for some time after copulation before 

 they are used, and the ova are presumably fertilized soon after 

 leaving the ovo-testis. 



Whenever the sperm-head is present in eggs from the oviduct, 

 it appears merely as a deeply stained oval body at the periphery 

 of the ^g^. There is no evidence of an attraction-cone having 



