189 



On the Spermatozoon of the Rat. 



By a. a. Merlin, F.R.M.S. 



{Taken as read November 15ih, 1901.) 



A few years ago, in microscoping difficult objects, the modus 

 opei'audi frequently consisted in first examining the specimen, say, 

 under a ^-in. or g-in. objective, and of then substituting a ^j in. 

 or -^-^ in. of probably little higher numerical aperture than the 

 lens previously employed. If no new detail was perceived 

 under the jjj in. it was taken for granted, as a matter of 

 course, that none existed, and the structure was confidently 

 described as homogeneous. It is now, of course, well known 

 that mere magnifying power per se without a corresponding 

 increase of the numerical aperture is of little avail ; and we 

 can no longer feel confident that because no structure is discern- 

 ible with an oil-immersion lens of N.A. 1*4, capable of yielding 

 a useful magnification of 1500, or at most 2000 diameters, that 

 therefore none exists. On the contrary, it hardly seems logical 

 to suppose that the numerous highly complex and imperfectly 

 understood processes just observable under our highest powers 

 and most perfectly corrected objective^ are not preceded by, 

 and dependent on, still minuter changes utterly beyond their 

 grasp. 



In consequence of the formerly prevalent opinion that structure 

 unresolvable by the old ^Q-in. and gVin. objectives, as then used, 

 must be altogether non-existent, the spermatozoa, originally 

 discovered by Leeuwenhoek about 1677, were by most considered 



JouRN. Q. M. C, Series II. — No. 50. 13 



