ONTOGENY 



11 



small actively motile cells termed sperm cells or microgametes. 

 A single sperm from one colony then meets and conjugates 

 with a single ovum from another colony, forming thus a single 



D 



FIG. 10. Reproduction in the colonial Flagellate, Volvox. A. After Prings- 

 heim, B-E, after Klein and Schenck. A. "Young colony showing distinction 

 between, s, somatic cells, and g, reproductive cells (parthenogonidia). B. Older 

 colony showing, p, parthenogonidia, o, oogonidia, sp, spermagonidia in various 

 stages of formation. C. Spermagonidium consisting of thirty-two spermagam- 

 etes, seen from the side in D. E. Spermagametes more highly magnified. 



cell or zygote, which through continued fission gives rise to the 

 individuals of a new colony. 1 



1 Useful diagrams of these forms of reproduction and gamete formation 

 are given in HEGXER, "An Introduction to Zoology," New York, 1910, pp. 

 112-115. 



