THE SPERMATOZOON 



99 



morphological nature as the ovum. It is of extraordinary minuteness, 

 being in many cases less than yooVoo ^^^ ^^^^^ ^^ ^^^ ovum.^ Its 

 precise study is therefore difficult, and it is not surprising that our 

 knowledge of its structure and origin is still far from complete. 



Apex or apical body. 

 Nucleus. 



End-knob (?centrosome). 

 Middle-piece. 



Envelope of the tail. 

 A.xial filairent. 



I. Flagellate Spermatozoa 



In its more usual form the animal spermatozoon resembles a 

 minute, elongated tadpole, which swims very actively about by the 



vibrations of a long, slender tail morpho- 

 logically comparable with a single cilium 

 or flagellum. Such a spermatozoon con- 

 sists typically of four parts, as shown in 



Fig. 47 • — 



1. The nucleus, which forms the main 

 portion of the "head," and consists of a 

 very dense and usually homogeneous mass 

 of chromatin staining with great intensity 

 with the so-called " nuclear dyes " {^e.g. 

 haematoxylin or the basic anilines such as 

 methyl-green). It is surrounded by a very 

 thin cytoplasmic envelope. 



2. A minute apex, or apical body, as a 

 rule of cytoplasmic origin, though appar- 

 ently derived in some cases from the 

 nucleus. This lies at the front end of 

 the head, and in some cases terminates 

 in a sharp spur by means of which the 

 spermatozoon bores its way into the ovum. 



3. The middle-piece, or connecting piece, 

 a larger cytoplasmic body lying behind the 

 head and giving attachment to the tail. 

 This body shows the same staining-reaction 

 as the tip, having an especial affinity for 

 "plasma-stains" (acid fuchsin, etc.). 



4. The tail, ox flagclhivi, in part, at least, 

 a cytoplasmic product developed from or 

 in connection with the " archoplasm " (at- 

 traction-sphere or "Nebenkern") of the 



mother-cell. It consists of a fibrillated axial filament surrounded 

 by an eiivelope which sometimes shows a fibrillar structure, sometimes 

 winds spirally about the axial filament, and is in certain cases diffcr- 



1 In the sea-urchin, Toxopnetistes, I estimate its bulk as being between juoVoo a^d 

 ^__i___ the volume of the ovum. The inequality is in many cases very much greater. 



■ Knd-piece. 



I 



Fig. 47. — Diagram of the flagel 

 late spermatozoon. 



