MASTIGOPHORA 



37 



reproduction by division into 4 or 8 cells, which remain in the shell and 

 then become free: 2 species. 



P. uvellum Ehr. (Fig. 47). Length .02 mm. : in . 



fresh water. 



f 



SUBORDER 3. YOLVOCINA. 



Colonial flagellates, the individual cells of uvellum 



which have each 2 flagella, an eye-spot and green 



chromatophores, and are imbedded in a common cellulose jelly; repro- 

 duction sexual and asexual: 7 genera, all represented in America; in 

 fresh water. 



Key to the genera of Volvocina: 



<*! Colony in form of a plate. 

 &! Flagella on one side only of colony. 



G! Colony squarish 1. GONIUM 



c 2 Colony round with a spheroid envelope 2. STEPHANOSPH^EA 



6 2 Flagella on both sides 5. PLATYDORINA 



a 2 Colony spherical or ellipsoidal. 

 &! Colony microscopic. 



G! Cells crowded, reaching center of colony 3. PANDOBINA 



c 2 Cells not thus crowded. 



d t Cells alike in size 4. EUDOEINA 



d z Anterior cells small, posterior ones large 6. PLEODORINA 



& 2 Colony not microscopic and composed of a large number of cells ... 7. VOLVOX 



1. GONIUM 0. F. Miiller. Colony of few and similar individuals 



forming a squarish plate with the flagella on one 

 face only; asexual reproduction by repeated divi- 

 sion of all the cells, each forming a new colony; 

 sexual reproduction the result of the conjugation 

 of pairs of similar individuals, the zygotes thus 

 formed, after a resting stage, each developing into 

 a colony : 2 species, 1 American ; in fresh water. 



G. pectorale 0. F. Mill. (Fig. 48). Colony 

 consists of 16 cells and .06 mm. in diameter: 

 cosmopolitan. 



2. STEPHANOSPHJERA Cohn. Colony consisting of 4 or 8 cells ar- 

 ranged in a ring which is surrounded by a large rounded envelope of 

 which the cells form the equator; reproduction as in Gonium: 1 species. 



S. pluvialis Cohn. Envelopes up to .06 mm. in diameter. 



3. PANDORINA Boxy de Vincent. Colony more or less spherical, 

 composed of 16 or 32 crowded cells which reach the center and are sur- 

 rounded by a lamellate envelope; reproduction as in Gonium , except that 

 the conjugating cells may differ slightly in size : 1 species. 



Fig. 48 



Gonium pectorale 

 (Doflein). 



