154 THE TESTES, BY V. LA VALETTE ST. GEORGE. 



elongation and flattening. A separation is then visible between 

 an anterior darkly contoured and a posterior somewhat smaller 

 pale-edged portion. Thus, whilst in many instances a very 

 small dark capitate thickening is seen at the anterior pole, a 

 short thread-like appendage makes its appearance at the 

 posterior, which soon forms a long tail, and at the same time 

 the paler posterior part of the nucleus continuously diminishes 

 in size. The fully developed zooid lies for some time longer 

 coiled up in the mother cell, and usually frees itself by the 

 head bursting through one part and the tail through the oppo- 

 site. Fragments of the mother-cell remain attached to the 

 spermatozoon for a little while longer, partly as a cap-like 

 appendage, but especially adherent to the tail. Kblliker finally 

 gives the following resume of his views respecting the develop- 

 ment of the spermatozoa throughout the animal kingdom : 



1. The fertilizing agents of all animals are developed by the 

 direct conversion of the nuclei of the sperm cells. 



2. The motionless seminal bodies of the Arachnida, Myria- 

 pods, etc., are simply modified or morphologically altered 

 nuclei. 



3. In the case of the active seminal bodies, or spermatozoa, 

 besides the body of the zooid, a movable fibre is developed 



' from the nucleus. 



Ankermann* considers that in the Frog every spermatozoon 

 is developed from a nucleated cell. The nucleus forms the 

 head, whilst the tail originates in a protrusion of the cell 

 membrane. 



Pfluger-f* regards the spermatozoa as small ciliated cells, and 

 refers their origin to a process of free cell formation. 



Henle^ agrees with Kolliker in believing the body of the 

 spermatozoa in Man and Mammals to be a metamorphosed 

 nucleus, but thinks that a persistent connection of the body 

 with the cell is indispensable for the formation of the tail. 



Grohe considers it to be probable that the contractile sub- 



* Zeitschrift fur wissenschaft. Zoologie, Band viii. , p. 129. 



f Ueber die Eierstocke, p. 93. 



J Handbuch der Eingeweidelehre, p. 356. 



Loc. cit., p. 226. 



