234 bulletin: museum of comparative zoology. 



tozoa have always been present surrounding the egg and completely 

 filling the oviduct. This condition suggests simultaneous movement of 

 the eggs and spermatozoa from the hermaphrodite gland. I have never 

 found either eggs or spermatozoa alone in the oviduct. 



Under these conditions one might expect self-fertilization, and I have 

 looked carefully for evidence of it. That self-fertilization has not taken 

 place, at least in the oviducal eggs that I have examined, may be 

 explained by what seems to be a fact, viz. that the spermatozoa occu- 

 pying the oviduct are in an immature condition. In the developing 

 sperm element, as the head of the spermatid begins to take on the 

 form characteristic of the mature condition, the tail is continually grow- 

 ing in length. The end of the tail of the spermatid exhibits a large 

 knob. In the fully developed free spermatozoon there is no indication 

 of this knob. Now, in the oviducal spermatozoon of Limax agrestis I 

 have seen this knob-like structure and I am inclined to think all the 

 spermatozoa in the oviduct are in this immature condition. 



So far as I know, the spermatozoon has never been observed in the 

 act of penetrating the egg in gasteropods. It is not very important, 

 however, in gasteropods that this phenomenon should be observed, since 

 the tail in following the head into the egg affords the observer the 

 means of determining the topographical relations necessary for noting 

 certain preliminary processes of fertilization.^ 



In the case of Limax maximus I have found, in one instance, a sper- 

 matozoon very near the periphery of the egg, w^hich it apparently had 

 but recently penetrated, while the first maturation spindle was migrat- 

 hig to the periphery to form the first polar cell (Plate 3, Figure 16). 

 When, in other instances, the spermatozoon was in practically the same 

 stage as represented in the figure just mentioned, I have found the first 

 polar cell completely formed (Plate 3, Figure 21). In one instance 

 (L. agrestis, Plate 3, Figure 14) I found the spermatozoon with head 

 and tail still connected, and the germinative vesicle of the egg just dis- 

 appearing. Kostanecki und Wierzejski ('96) found in Physa that a 

 spermatozoon may penetrate the egg and a large sperm-aster may be 

 developed by the time the first maturation spindle is formed. On the 

 other hand, they found that, in the same species, the spermatozoon may 

 not penetrate the egg until both polar cells have been formed. 



1 I may anticipate criticism of this statement by calling attention to what is 

 probably a fact, that tlie viscidity of the egg-cytoplasm prevents great whiplash 

 movements of the spermatozoon; it is not likely therefore that the tail is "fixed" 

 in a position far from the path along which the spermatozoon has progressed. 



