352 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



The nuclei of the sperm morula, which, when first 

 formed, are scattered irregularly through the cell, 

 gradually become arranged more regularly around the 

 periphery of the cell, the central portion of which has no 

 nucleus and is, therefore, entirely cytoplasmic in nature. 

 The cytoplasm surrounding the nuclei at the periphery of 

 the sperm morula exhibits slight cleavage marks around 

 each nucleus, and these cleavages deepen until the nuclei 

 are completely constricted off from one another, while 

 still remaining in connection with the cytoplasmic mass 

 occupying the centre of the morula, which remains 

 undivided throughout and is known as the sperm blasto- 

 phore (PL Y, figs. 30 and 31). During this protoplasmic 

 cleavage the sperm morula or sperm polyplast increases 

 considerably in size, and the nuclei are large, rounded, 

 and possess nucleoli. Each of the elements making up the 

 fully formed sperm morula is called a spermatocyte, and 

 these are at first large and comparatively few in number 

 (PI. V, fig. 31). The spermatocytes are arranged 

 extremely regularly around the sperm blastophore, but 

 this arrangement can only be fully appreciated when the 

 sperm morula is viewed in section (PL V, fig. 32). 



The nucleus of each of the spermatocytes now under- 

 goes karyokinetic division, probably twice, and the cells 

 then divide so that the number of elements comprising a 

 sperm morula in its later stages of development is very 

 much increased. The cells thus formed are much smaller 

 than the spermatocytes, as there is no appreciable increase 

 in the size of the whole morula at this stage (PL V, 

 fig. 33). The cells resulting from the division of the 

 spermatocytes are known as spermatids, and from these 

 the mature spermatozoa are derived by a simple meta- 

 morphosis. The spermatids are at first rounded in shape, 

 and the nucleus forms the greater part of the cell, the 



