No. 3. J SPERM ATOPHORES. 381 



surface ; and an inner, denser, thicker, stainable layer (Fig. 2, i). 

 The outer layer is so extremely thin over the saccular portion 

 of the fresh spermatophore that it is difficult to recognize it ; ^ 

 but it is easily demonstrated on sections. In the basal portion, 

 this layer thickens, and then expands to form a broad base, so 

 closely applied to the underlying cuticula as to form almost a 

 continuum with it (Fig. 2). The striations of this layer may be 

 due to the pull given to the sac as it is liberated from the 

 genital pore, or more probably, as I think, to its mode of forma- 

 tion by numerous gland-cells. 



When first placed, the spermatophore usually stands nearly 

 perpendicular to the surface. It is tough and elastic, and con- 

 siderable force is required to detach it. The skin of the leech 

 around the place of attachment is at first strongly corrugated, 

 as if by contraction ; but this appearance gradually passes away 

 after the sac is emptied, although the sacs often remain for 

 several days, or even weeks. Whether they are ultimately dis- 

 solved, or shed with the cuticula, or drop off as the result either 

 of vital processes in the underlying skin, or of the solvent action 

 of water, I am unable to say. 



The mouth of the fresh spermatophore is completely plugged 

 with a peculiar secretion (Fig. 4, a, gs), made up of elongated ellip- 

 tical or spherical corpuscles (Fig. 4, c), varying from 0.02 mm. in 

 diameter to much smaller dimensions. These bodies dissolve 

 in water in the course of a few minutes. At first appearance, 

 they are coarsely granular, but rapidly become perfectly homo- 

 geneous and transparent, and, growing paler and paler, fade 

 away by insensible degrees. At first I took these bodies to be 

 cells, as some of them appeared to be nucleated ; but having 

 traced them to their origin in glands of a definite region of the 

 vasa deferentia, I now think that the nucleus-like centre (Fig. 

 4, c) merely marks the depth to which the water had penetrated 

 at the moment of examination. Their great variation in size 

 is also in harmony with their origin as globular secretions. 



This granular secretion probably serves a double purpose : 

 first, to protect the spermatozoa inclosed in the saccular portion 

 against contact with water ; and secondly, as a means of open- 

 ing and clearing the way for the safer penetration of the sper- 



1 Exposed to acetic acid, it swells, and is thus made evident without the aid of 

 sections. 



