(Fig. 21). In a surface view, the head has an 

 oval form, but the anterior half is much flattened, 

 and when seen in profile shows a fine pyriform 

 extremity. The anterior part of the head is 

 enclosed in a membrane (galea capitis) which 

 terminates in a transverse line between the 

 anterior two thirds and posterior third of the 

 head. A; very short segment of transparent 

 substance, the neck, forms a continuation to the 

 head. In the neck are observed two granules 

 (centrosomes) which, as we shall see, have a most 

 important function in fertilisation. The neck 

 is continued in an intermediate segment in the 

 form of a small rod which is followed by the 

 principal part of the tail and the terminal part, 

 which is very fine. 



The spermatozoon (first discovered with the 

 microscope by Hammer, a pupil of Leeuwenhoek, 

 in the human semen in 1677) has the morpho- 

 logical significance of a cell ; the head represents 

 the nucleus of the seminal cell, the neck and 

 intermediate segment represent the protoplasm 

 (fibrillary) containing the centrosomes and the 

 caudal filament the protoplasm (fibrillary) with- 

 out centrosomes. 



The quantity of semen which is emitted at 

 each ejaculation varies from a minimum of 0'85 

 c.c. to a maximum of 5-6 c.c. On an average one 

 may assume a quantity of 3 c.c. (Mantegazza, 

 Lode). In successive ejaculations within the 

 space of twelve hours, the quantity of seminal 

 fluid progressively diminishes from the maximum 

 to the minimum ; but in the interval of only a 

 day between one ejaculation and another, the 

 quantity of the secretion in the healthy adult 

 man returns to the normal average. The specific 

 gravity of the semen varies, according to Lode, 

 from 1027 to 1046; the average is. 1036. In 

 the state in which it is emitted it appears as a 

 viscous liquid, tenacious, whitish, with an alkaline 

 reaction, and a specific odour due to the prostatic 

 secretion with which it is mixed. In the first 



fin. 21. A typical human spermatozoon, extended in rectilinear posi- 

 tion. A, with the head seen in sujmrflcies ; Ji, with the head seen in 

 profili'. (Het/ins, 1'.'02.) o, anterior part of the head and cowl (in 

 A is seen also a little dark point) ; p, posterior part of the head ; c, 

 neck with centrosomes ; i, intermediate piece, jwrt connecting with 

 tail ; pr, principal part of the tail ; t, terminal part of the tail. 



ft 



