I BROOD-FORMATION COLONIES 3 I 



increased, hence it has received the name of " sporulation." The 

 term spores is especially applied to the reproductive bodies of 

 Cryptogams, such as Mosses, Fungi, etc. : the resulting cells are 

 called " spores," " zoospores " if active (" amoebulae " if provided 

 with pseudopodia, " flagellulae " if flagellate), " aplanospores," if 

 motionless. We prefer to call them by the general term " brood- 

 cells," the original cell the " brood-mother-cell," and the process, 

 " multiple fission " or " brood-formation." As noted, the brood- ■ 

 mother-cell usually attains an exceptionally large size, and it in 

 most cases passes into a state of rest before entering on division : 

 thus brood-formation is frequently the ultimate term of a long 

 series of Spencerian divisions. Two contrasting periods of 

 brood-formation may occur in the life cycle of some beings, 

 notably the Sporozoa.^ 



Colonial union. — In certain cases, the brood-cells instead of 

 separating remain together to form a " colony " ; and this may 

 enlarge itself again by binary division of its individual cells at 

 their limit of growth. Here, certain or all of the cells may 

 (either after separation, or in their places) undergo brood- 

 formation : such cells are often termed " reproductive cells " in 

 contrast with the " colonial cells." 



Some such colonial Protista must have been the starting- 

 points for the Higher Animals and Plants ; probably apocytial 

 Protista were the starting-points of the Fungi. In the Higher 

 Animals and Plants, the spermatozoa and the oospheres (the male 

 and female pairing-cells) are alike the offspring of brood-formation: 

 and the coupled -cell (fertilised egg) starts its new life by 

 segmentation, which is a brood-formation in which the cells do 

 not separate, but remain in colonial union, to differentiate in 

 due course into the tissue-cells of the organism. 



Retarded brood -formation. — The nuclear divisions may 

 alternate with cell-divisions, as above stated, or the former may be 



1 One obvious effect of brood-formation is to augment rapidly the ratio of 

 superficial area to bulk: after only three divisions (p. 23, note) the ratio is 

 doubled ; if the divisions be nine in succession so as to produce a brood of 512, the 

 ratio is increased eightfold, on the supposition that the figure is preserved. Plow- 

 ever, the brood -mother -cell is usually spherical, while zoospores are mostly 

 elongated, thus giving an additional increase to the surface, which we may 

 corrSate with that increased activity; so that they disseminate the species, 

 spreading far and wide, and justifying the. name of "spore" in its primitive sense 

 (from the Greek a-n-dpa—l scatter [seed]). 



