382 WHirMAN. [Vol. IV. 



matozoa. This mass is expelled through the skin in advance of 

 the spermatic elements ; and the disappearance of the pigment 

 and the clarification of the tissues at the point of penetration, 

 all of which is noticeable in sections (Fig. 2), suggest that it 

 may have a softening effect on the tissues.^ This, however, is 

 pure conjecture. With plenty of material, the action of this 

 secretion on fresh pigmented tissue might possibly be deter- 

 mined experimentally ; but thus far I have not tried this. 



If the leech is placed under a magnifying power of twenty or 

 forty diameters, immediately after receiving one of the sperma- 

 tophores, one may see the spermatozoa slowly flowing from the 

 narrow mouth of the case through the skin. In the course of an 

 hour the greater part of the contents has escaped, and the case 

 itself is reduced to less than half of its original diameter. As 

 soon as the case is planted, it begins to shrink ; and this con- 

 traction, induced by the action of the water, is probably what 

 forces the spermatic fluid through the skin. When the sac is 

 first placed, the spermatozoa may be seen through the wall united 

 in close bundles. Soon after deposit, as one may see towards the 

 free end of the sac, these bundles begin to swell up, and the indi- 

 vidual spermatozoa begin to show themselves. The appearance 

 might raise a suspicion that a part of the spermatozoa undergo 

 histolytic changes, serving by expansion as a means of expelling 

 the rest, somewhat as described by Gruber in the Copepoda 

 (v. extract). I think, however, that Leuckart's suggestion in 

 regard to the spermatophore of Astaais is the explanation to be 

 adopted here, as it is perfectly certain that the sperm-case 

 gradually contracts as its contents escape. I find that a few 

 spermatozoa are always left in the case after it has reached the 

 limit of contraction, showing that the expelling force ceases to 

 act after this. As distinct spermatozoa were found in a sperm- 

 sac two days old, I infer that the sac is water-proof. If a 

 fresh sac be detached and exposed to the pressure of a cover- 

 slip, the sperm is rapidly driven out in the form of a white flaky 

 string, consisting of a viscid fluid, with numerous bundles of 

 spermatozoa. 



In order to learn precisely where the spermatophore is formed, 

 as well as the origin and relative positions of the various ele- 

 ments with which it is to be charged, it will be necessary to 



1 Isjima's observations on Nephelis favor this view. 



