DESCRIPTION OF THE SEXUAL PRODUCTS. 19 



and which constitute the dower that is given by the maternal 

 organism to the developing germ on its way. Thereupon the whole 

 is enclosed in one or several secondary egg-membranes, and now 

 constitutes the compound egg, in which, however, the developmental 

 processes manifest themselves exclusively on the simple germ cell ; 

 it is that alone which is fertilised and segments, while the yolk-cells 

 gradually degenerate and are employed as nutritive material. Thus 

 in this case also, upon closer examination, the general law, that the 

 descendent organism takes its origin from a single cell of the maternal 

 body, suffers no exception. 



2. The Seminal Filaments. 



In contrast with eggs, which are the largest cells of the animal 

 body, the sperm-cells or sperm -filaments (spermatozoa) are the 

 smallest elementary parts ; they are accumulated in great multitudes 

 in the seminal fluid of the male, but can be recog- 

 nised in it only by the aid of high magnification, 

 being, for the most part, slender motile filaments. 

 Inasmuch as every cell consists of at least two 

 parts, namely, nucleus and protoplasm, we must 

 look for these parts in this case also. We shall 

 take for description the spermatozoa of Man. 



In Man the seminal filaments (fig. 9) are about 

 O05 mm. long. One may distinguish as head (k) 

 a short but thick region, which marks the anterior 

 end, as tail a long thread-like appendage (s), and 

 between the two a so-called middle piece (ra). seen in two dif- 



The head (k) has the form of an oval plate, ^jg^ 

 which is slightly excavated on both surfaces, head (*), a mid- 

 and is somewhat thinner toward the anterior end. ^ |^ ece ( " i)> anc 

 Seen from the side () it presents a certain re- 

 semblance to a flattened pear. Chemically considered, it consists of 

 nuclear substance (nuclein or chromatin), as microchemical reactions 

 show. To the head is united, by means of a short part called the 

 middle piece (m), the long thread-like appendage (*), which is com- 

 posed of protoplasm, and is best compared to a flagellum, because, 

 like the latter, it executes peculiar serpentine motions in virtue of 

 its contractile properties. By means of these motions the sper- 

 matozoon moves forwards in the seminal fluid with considerable 

 velocity. 



