THE VITAL PHENOMENA OF THE CELL 



229 



nuclear spindle, with a polar radiation at each end, develops out of 

 its contents. This changes its position in the yolk (Fig. 118 I.), 

 raising itself gradually towards the animal pole, until its end 

 touches the surface. It then arranges itself with its longitudinal 

 axis in the direction of a radius of the egg. Cell-budding soon 

 commences at the place where one of the poles of the nuclear 

 figure touches the surface ; the yolk arches itself up to form a 

 small knob, into which half of the spindle protrudes itself (Fig. 

 118 II). 



The protuberance then becomes constricted at its base, and, 

 with half of the spindle, separates itself from the yolk, forming a 

 very small cell (Fig. 118 III.). Then the whole process repeats 

 itself (Fig. 118 IF.-FI.), the half of the spindle which has re- 

 mained in the egg, without previously passing through a resting 

 vesicular or nuclear condition, developing first into a complete 

 spindle. This process, as far as it refers to the nuclear spindle, 

 will be entered into at more detail on p. 237. 



Cell-budding occurs frequently amongst certain species of uni- 

 cellular organisms. I will select from amongst these a second 

 example, which has been examined by Richard Hertwig (VI. 

 35), the Podophrya, gemmipara, a marine Acineta, which attaches 

 itself by means of a stalk at its posterior end to other objects. 

 From eight to twelve cell-buds not infrequently develop at its 

 free end, which is provided with prehensile tentacles and suction 

 tubes ; these cell-buds are grouped in a ring around the centre of 

 the free surface. In this case, the nucleus divides in a peculiar 

 fashion. As long as the 

 Podophrya is young, and 

 has not yet commenced 

 to bud, the nucleus has, 

 as in so many Ciliata, 

 the form of a long horse- 

 shoe-shaped twisted band 

 (Fig. 119 6). Later on, 

 a large number of pro- 

 cesses grow out in a ver- 

 tical direction, towards 

 the free surface of the 



body ; their ends SOOll FIG. 119. Cell-budding, PodopTirya gemmipara, 



OW All nnt into "knobs with buds (O ' Hertwi S' Zoology, Fig. 21); o buds, 

 swe11 D8 ' which become detached and form zoospores b ; N 



whilst the portion of the nucleus. 



