II 



PHYLUM PROTOZOA 



75 



which they are finally liberated. In Vohox (Fig. 5 6), certain zooids, 

 called parthenogonidia (A, ), have specially assigned to them 

 the function of asexual reproduction: they divide by a process 

 resembling the segmentation of the egg in the higher animals 

 (D 1 -!) 5 ), and form daughter-colonies which become detached and 

 swim freely in the interior of the mother-colony. 



A very interesting series of stages in sexual reproduction is 

 found in this group. In Heteromita two individuals come together 



A, entire colony, enclosing several daughter-colonies; 

 urity ; C, four zooids in optical section ; Dl D5, develop- 



Fio. 5tj. Volvox erlobator. 



B, the same during sexual matxirity; 



ment of parthenogonidhim ; E, ripe spermary ; F, sperm ; G, ovary containing ovum and 

 sperms ; H, oosperm ; a, parthenogonidia ; A. flagellum ; oc. ovum ; ofy. ovaries ; pg. pigment 

 spot ; spy. spermaries. (From Parker's Biology, after Cohn and Kirchner.) 



(Fig. 57, E 1 ) and undergo* complete fusion (E 2 E 4 ) : the result of 

 this conjugation of the two gametes or conjugating cells is a thin- 

 walled sac, the zygote (E 5 ), the protoplasm of which divides by 

 multiple fission into very minute spores. These, when first 

 liberated by the rupture of the zygote (E 6 ), are mere granules, 

 but soon the ventral or trailing flagellum is developed, and after- 

 wards the anterior flagellum (F 1 F 4 ). In Pandorina (Fig. 55) 

 the cells of the colony escape from the common gelatinous envelope 

 (C) and conjugate in pairs (D, E), forming a zygote (F, G), which, 

 after a period of rest (H), divides and forms a new colony (K). 



