EMBRYOLOGY.^ 
The Structure of the Human Spermatozoon. — Any new 
light which is thrown upon the structure of the sexual elements by 
the aid of more refined methods of research, will be welcomed in 
view of the possible bearings which such information may have upon 
questions of inheritance. That variations in the structure of the 
male elements do occur as abnormalities seems to be established by 
the researches of E. M. Nelson ^ who finds that not only do they 
vary in the number of heads, but also in the number of tails and 
even as to the number of the nuclei; forms were also met with which 
were joined together in pairs by a band. Those familiar with Se- 
lenka's work on the Opossum will recall in this connection the sin- 
gular fact recorded by that embryologist as to the double nature of 
the fresh spermatozoa of Didelphys virginiana. 
The most interesting facts, however, which Mr. Nelson records as 
the result of his studies, with the aid of the new apochromatic 
objectives of Zeiss, relate to the details of structure of the human 
The head, which has always been figured as a simple, somewhat 
flattened pyriform body, according to this last observer, is rather 
complex when studied by the aid of better appliances. It is rather 
obovate in outline from the broad side, but when viewed edgewise it 
is seen to be curved upon itself, so that it bears a resemblance to 
an oblong meniscus lens. 
Furthermore, this observer gives names to its parts. The anterior 
portion containing the nucleus, he calls the spore, and at its extreme 
anterior pole it bears an excessively xi\\ww\.Q filament as he names it, 
which is hardly as long as the spore itself. He suggests that this is 
a sort of feeler or tentacle by means of which the spermatozoon finds 
Its way into the pore in the ovum which serves for the micropyle. 
The flattened and curved fiagellum-bearing spore is joined to or 
rests in what Nelson calls the cup which corresponds to the swollen 
basal part of the head as usually figured. 
Then succeeds a delicate cycle of processes just around the base 
of the cup where the latter joins what Nelson calls the stetn, which 
answers to the "middle piece" of authors. This delicate cycle of 
bluntly rounded processes he calls the calyx. 
Next follows the stem or "middle piece " which at its posterior 
extremity is slightly swollen. This swollen posterior extremity of 
the stem and the anterior end of the tail there occurs a constriction 
which has been previously noticed by Nelson, and to which he gives 
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