THE GAMETES 3I 



morphology, seeRetzius 1902-1909.) The processes of formation of these 

 speciaHsed parts of the cells have been the object of considerable micro- 

 scopial study (c£ Gresson 1948) but the results have not been very clear 

 cut, nor have different investigators always reached agreement. This is 

 nov^adays not so surprising, since studies with the electron microscope 

 have shown that sperm contain many structures which are well below 

 the resolving power of the hght microscope, so that studies with the latter 

 could not be expected to reveal the mode of their formation. The electron 

 microscope work is still in its infancy, and again it is the case that agree- 

 ment on the structures has not yet been reached. What is important is that 

 this new tool has shown that the material architecture of the sperm is 

 certainly very much more comphcated than had been suspected. An indi- 

 cation of the degree of complexity involved may be had from Fig. 2.2, 

 which shows the structure of the middle piece of a ram's sperm, as inter- 

 preted by Randall and Friedlaender (1950). Even if some revision later 

 turns out to be necessary to this picture, it is impressive to discover that 

 such an apparently simple object can contain so many structurally distinct 

 components arranged in such defmite and elaborate patterns. 



The spermatozoon is a small light cell, capable of independent move- 

 ment. It plays the active role in fertilisation, in contrast to the immobile 

 and passive egg. This activity is, in fact, the basic definition of a male 

 gamete ; in some organisms the sperm is very unHke the common pattern 

 just described, and in lower plants, for instance, there may be very Httle 

 difference in shape between the female and male gametes ; but wherever 

 there is a difference in activity, we say that the more active type is the 

 male, the less active the female. "Whether there is any more fundamental 

 similarity, other than their activity, between the male gamete of an Alga 

 and a mammalian spermatozoa, remains rather a debatable question. 



The metabohsm of sperm is being very actively studied at the present 

 time, both for its own intrinsic interest, and on account of its importance 

 for the technique of artificial insemination. Reviews of recent work on 

 mammalian semen and sea-urchin sperm will be found in Mann (1949, 

 1954) and Rothschild (195 id). 



2. Oogenesis 



The formation of the egg-cell is a more comphcated and more lengthy 

 process than the formation of the sperm. As a bearer of a haploid nucleus, 

 the ovum has a somewhat simpler task than the sperm, since it does not 

 need to produce any means of locomotion. But this simplification is more 

 than outweighed by the fact that it is out of the cytoplasm of the ovum 

 that the main structures of the embryo must be formed. The egg must 



