622 PATTERNS AND PROBLEMS OF DEVELOPMENT 



male gamctophyte, the third giving rise to spermatozoids. This pattern 

 is presumably determined in the microsporangium. The polarity of the 

 grain is also evident in its germination and formation of the pollen tube 

 at the small-celled pole. In the tube the generative nucleus divides with 

 spindle transverse to the long axis of the tube, forming two hemispherical 

 cells. In each of these the blepharoplast, described as derived from the 

 centrosome, elongates, becomes spirally coiled anticlockwise, and gives 

 rise to a band of cilia (Fig. 197, B, C). The axis of coiling coincides with 

 the spindle axis of the preceding division ; the ciliated part of the sperma- 

 tozoid develops from the region about the pole of the last spindle; and 

 the rounded, nonciliated part from the flattened cell surface in contact 

 with the sister cell.^ The spermatozoid axis is at right angles to the axis 

 of the pollen grain and pollen tube and is apparently determined by some 

 factor correlated with division of the spermatogenous cell, since it coin- 

 cides with the axis of the spindle and is indicated by the hemispherical 

 form of the spermatid and by position of nucleus and centrosome; and 

 this division is definitely related to the axis of the pollen grain and tube. 

 In short, each step in development of the polar pattern appears in a defi- 

 nite relation to a pre-existing pattern. The spiral of the blepharoplast 

 appears only secondarily and in a definite relation to the polar axis. 

 During early development of the spiral band a beaklike extension of the 

 nucleus becomes closely associated with the blepharoplast, as if it were 

 about to elongate and become spiral, as in the spermatozoids described 

 above; but this association is only temporary, and the nucleus does not 

 become spiral. The male nuclei of various seed plants, however, do de- 

 velop a more or less pronounced spiral form preceding fertilization (Fig. 

 igj, D,E). 



ANIMAL SPERMATOZOA 



The great variety of form, the spirals, and specific asymmetries of ani- 

 mal spermatozoa have long been familiar to students of spermatogenesis. 

 The spermatozoa of Figures 198-200 show fully developed spermatozoa 

 of turbellaria (Fig. 198, A-C), a nematode (Fig. 198, D), a gasteropod 

 (Fig. 198, E), an annelid (Fig. 198, F), the more or less radial spermatozoa 

 occurring among Crustacea (Fig. 199, A-C), a spider (Fig. 199, D), a 

 beetle (Fig. 199,. £), a fish (Fig. 200, A),2l salamander (Fig. 200, B), and 

 a toad, with undulating membrane, resembling somewhat that of a try- 

 panosome (Fig. 200, C). In certain entomostraca the spermatozoa are 

 spherical cells; those of some others are amoeboid, according to Weismann 



» Ikcno, 1898; Webber, 1901. 



