E. M. NELSON ON THE HUMAN SPERMATOZOON. 311 



diseases of a grandfather, and does not feel in the presence 

 of a mighty force, must be indeed, steeled to insensibility. It 

 is strange that this object, so interesting on account of its 

 intimate connection with ourselves, should have been so slovenly 

 microscoped. The drawings of the human spermatozoon are 

 only up to the microscopy of early achromatic days. A few 

 years ago special attention was given to this object by the 

 announcement that a dorsal appendage had been observed 

 on the tail of the human spermatozoon, similar to that on 

 the newt. # I went into the matter very carefully at that 

 time with the best lenses and apparatus of that day, but 

 failed to see any such appendage. Further, the author of the 

 paper showed me the specimens, but was unable to demonstrate 

 the dorsal appendage. While working at this question I dis- 

 covered the joint in the tail, or, more strictly speaking, at the 

 point where the tail is joined to what I have termed the stem, 

 and this discovery I communicated to the Club in 1882. Since 

 that date, thanks to the Abbe Zeiss' apochromatics, the curtain 

 which hides the very small from our gaze has been drawn up a 

 little higher. I am, on this account, in a position to put before 

 you a more complete description of this interesting object. 



Before entering on this description, however, it is necessary 

 to point out that there are great variations in the form of the 

 spermatozoa. The drawing I now place before you is that of a 

 type constructed from a careful consideration of a great number 

 of slightly differing forms. 



Spermatozoa may appropriately be likened to mushrooms. 

 No two mushrooms are precisely alike : one has a longer stem 

 than another, one a thicker stem, and so on ; but there is a pecu- 

 liar point in which mushrooms differ from one another and 

 which has its exact counterpart in the spermatozoon. Where 



* "Quar. Jour. Micro. Sci.," Vol. xx, n.s., No. 79, July, 1880 ; see also 

 Vol. xix, n s., No. 76, October, 1879. I find that the dorsal appendage 

 does not extend beyond the tail, as shown in the plate, but merges into it 

 near the point. The description in the letterpress is also misleading, as it 

 describes a filament joined to the " body " (which I have called " the tail ") 

 by a membrane. In reality there is no filament. What has been mistaken 

 for a filament is the microscopical appearance of the edge of the membrane. 

 An edge is always thickened and blackened in the microscope. This is, 

 therefore, an error not only in a certain special case, but in the fundamental 

 principles of the interpretation of microscopical images, and is one that is 

 repeatedly made. I am acquainted with a certain organism erroneously 

 figured and described, and in consequence erroneously named, owing to this 

 very error in microscopical observation. 



