E. M. NELSON ON THE HUMAN SPERMATOZOON. 313 



xxiv, exhibit what may be termed an average amount of calyx. 

 Next we come to the stem, which is a short piece between the 

 cup and the tail proper. This is variable in thickness, being 

 sometimes much thicker than the tail and sometimes of the 

 same thickness. There is another variation in this part of the 

 spermatozoon. This occurs at the end of the stem immediately 

 preceding the break which I have called the joint. At this 

 point it usually thickens, though in some*' few instances I have 

 been unable to detect any such thickening. 



The joint is always present ; the amount of the opening, how- 

 ever, is variable. 



The connecting bar between the stem and the tail I have 

 drawn dark, as I see it ; it may not be necessarily any darker 

 tiian the stem or the tail ; the close approximation of its two 

 edges would account for its dark appearance. The upper part 

 of the tail is usually as shown in the figure, but occasionally I 

 have found a thickening similar to that at the end of the stem. 

 The upper part of the tail is, on the average, slightly thinner 

 than the stem. On the tail I have not been able to detect the 

 smallest appearance of a dorsal appendage. The tail I should 

 regard as fairly constant in thickness and length ; on this point 

 I speak from estimation, not from measurement. I have now 

 another new feature to bring before you, and that is the discovery 

 of a filament on the spore. I use the term filament in contra- 

 distinction to flagellum, although it closely resembles that of 

 a bacterium, because I regard it as a director, pointer, or 

 kind of antenna for the purpose of guiding the spore into an 

 aperture in the ovum.* 



The filament is considerably finer at its root than the tail is 

 at its point. 



In the spore you will notice a nucleus with a divided nucleolus ; 

 this is drawn from actual observation. It w r ill form a kind of 

 test object, for unless you can see the division in the nucleolus 

 there is little chance of a sight of the filament. In the observed 

 example the division in the nucleolus w r as smaller than either 

 of the nucleoli themselves. After careful estimation I concluded 

 that it was a \ or \ of the diameter of one of the nucleoli. On 

 measurement I found the diameter of the nucleus was y^-inch 



* " Bees and Beekeeping," by F. E. Cheshire, "Vol. i, pp. 224, 231. The 

 spermatozoon of the bee has a larger but similar filament. In that of the 

 snail there is a very large one. 



