498 



TEXT-BOOK OF ENTOMOLOGY 



forms. There is a double-tailed type, already described by Biitschli and v. la 

 Valette St. George, and there are others which are single-tailed. Biitschli 

 showed that in the double spermatozoon one tail-filament is straight and stiff, 

 the other being undulating and contractile. Ballowitz describes this type in 

 Calathus (Fig. 470, J?), Chrysomela, and Hylobius, etc., and shows that the 

 straight or supporting portion of the tail is elastic, but somewhat stiff, resistant 

 to reagents, and without any fibrillar structure, while the contractile fringe 

 consists of. an extremely complicated system of fibrils (Fig. 470). The single- 

 tailed type of spermatozoon, as seen, e.y., in Melolontha and Hydrophilus, has 

 no supporting fibres. The tail is twisted in a spiral, corresponds to the con- 

 tractile fringe of the double type, and exhibits a complicated fibrillar structure. 

 The fringed type works its way ahead like the screw of a steamer. 



Each spermatozoon is a modified but complete cell, and the nucleus 

 contains the chromatin, a deeply staining substance of the nuclear 



network and of the chromosomes 

 and the supposed bearer of heredity. 

 Formation of the spermatozoon. 

 It arises from a primordial germ- 

 cell called spermatogoninm. This 

 cell contains a large, pale nucleus 

 and a dark body, the accessory nu- 

 cleus of Biitschli. The sperinato- 

 gonia subdivide, but at a certain 

 period pause in their subdivisions, 

 and undergo considerable growth. 

 "Each spermatogonium is thus 

 converted into a spermatocyte, 

 which, by two rapidly succeeding 

 divisions gives rise to four sperma- 

 tozoa, as follows: The primary 

 spermatocyte first divides to form 

 two daughter-cells, known as sper- 

 matocytes of the second order, 

 or sperm mother-cells. Each of 



nucleus; p, paramicleus; , envelope of the fV, 00 o rlivirlaa nrrain ia n vnlp 

 tail. -After Plainer, from Wilson. 



without pausing, and without the 



reconstruction of the daughter-nuclei to form two spermatids or 

 sperm-cells. Each of the four spermatids is then directly trans- 

 formed into a single spermatozoon ; its nucleus becoming very small 

 and compact, its cytoplasm giving rise to the tail and to certain 

 other structures. ... As the spermatid develops into the spermato- 

 zoon, it assumes an elongated form, the nucleus lying at one end, 

 while the cytoplasm is drawn out to form the flagellum at the oppo- 

 site end." (Wilson's The Cell, from La Yalette St. George.) 



FIG. 471. ("*, anterior end of spermatic! 

 of a moth ( Pygn-ra) . />, young spermatozoon 

 of the same ; af, axial filament ; c, centro- 

 some ; m, middle-piece or mitosoma ; n, 



