THE VITAL PROPERTIES OF THE CELL 273 



pearance ; the spermatozoon often contains less than 

 the protoplasm present in the ovum. Thus, according to Thuret's 

 computation, the ovum of Fucus is as large as from 30,000 to 

 60,000 antherozoids. In animal sexual cells, the difference is 

 usually still greater, especially when the egg-cells are copiously 

 laden with reserve materials, such as fat-globules, yolk-granules, 

 etc. Indeed, in typically developed spermatozoa the presence of 

 protoplasm at all may be doubted ; for the tail, which is attached 

 to the middle portion, consists of contractile substance, which, like 

 muscle fibres, is a differentiation product of the protoplasm of the 

 sperm-cell. In immature spermatozoa, protoplasm is present in the 

 form of drops of various sizes, which, having served their purpose 

 during development, eventually disappear. 



Nuclear substance behaves in quite a different way. However 

 much the ovum and spermatozoon may vary as to size, they still 

 invariably contain equal quantities of active nuclear substance. 

 The truth of the above statement cannot be proved by a simple 

 comparison of the two sexual cells, but if the course of the process 

 of fertilisation and of the development of the mature ovum and 

 sperm-cell be watched, it will be seen that they both contain an 

 equal quantity of nuclein, and that during the process of matura- 

 tion they develop an equal number of nuclear segments. For 

 example, the sperm-nucleus of Ascaris megalocephala bivalens con- 

 sists, like the egg-nucleus, of two nuclear segments of the mother 

 cell ; each during fertilisation contributes similar elements, which 

 are utilised in the formation of the germinal nucleus (Fig. 142 

 II). In the same way each nucleus contributes the same amount 

 of polar substance, the male and female centrosome both of which, 

 in the manner described on p. 262, take part in the process of 

 fertilisation (Fig. 141). 



In opposition to these conclusions, it might be stated, that the 

 nuclear portions of both egg and sperm-cells before their union 

 are usually very different in appearance, and vary more or less in 

 size. This, however, is easily explained by the fact, that the passive 

 fluid substances may be mixed in greater or less quantities with 

 the active nuclear substance. The minute head of the sperma- 

 tozoon consists of fairly compact, and hence strongly stainable, 

 nuclein. In the egg-nucleus, which is much larger, the same 

 amount of nuclein is saturated with a quantity of nuclear sap, 

 throughout which it is distributed in the form of minute granules 

 and threads, the result being that the egg-no cleus as a whole is 



T 



