THE MALE-CELL OR SPERMATOZOON. 



Ill 



the more important of these, the reader is referred to the Encyclopcedia 

 Britannica, article Reproduction. A few points only need be noticed here. 

 Thus most spermatozoa exhibit not only a head (almost wholly from the 

 nucleus of the mother-cell), and a mobile tail (from the substance of the 

 mother-cell), but a median portion connecting these. The tail is not 

 unfrequently, as in salamander and man, furnished with a very delicate 

 undulating or vibratile band. Complexities such as axial filaments, stria- 

 tions. and the like abound. In a few cases, as in the threadworm, the sperm 



Spermatozoa of crayfish {a), lobster {b), crab (c), ascarid (cf), 

 water-flea — moina {e), man (_/"), ray {g), rat 0i), guinea-pig 

 (z), a beetle — immature stage (Ji), sponge (/). 



is not left without any nutritive capital, but furnished with this in the form 

 of a cap, which falls off before the essential moment of fertilisation arrives. 

 Important perhaps is the observation, mainly due to Flemming, that the head 

 of the sperm not only arises from the nucleus of the mother-cell, but almost 

 wholly consists of the chromatin-elements of the same. 



§ 4. Physiology of the Spermatozoon. — A few facts in regard 

 to the physiology of the sperm demand notice, {a) It is 

 speciahsed as a highly active cell ; its minimal size, the usual 

 absence of any encumbering nutritive material, the contractility 

 of the tail, and the general shape, all fit it for characteristic 

 mobility. More than one histologist has likened it to a 

 free muscle-cell, and its resemblance to a flagellate monad ha3 

 already been noted, {b) Furthermore, the sperm has very 

 considerable power of persistent vitality. Not only does it 

 often remain long unexpelled in the male animal, without los-ng 

 its functions, but it may retain its fertilising power after remain- 

 ing for weeks, or even months, in the female organism. In the 

 earthworm, the spermatozoa pass from one worm to another, not 

 directly to the ova nor to female ducts, but to be stored up in 



