MASTIGOPHOEA 39 



7. VOLVOX* L. Colony forms a hollow sphere of large size and 

 composed of hundreds or thousands of cells connected by protoplasmic 

 threads, and not differing in size; asexual reproduction by so-called 

 parthenogonidia which are cells in the center of the colony (1 to 9 in 

 number), which form there by repeated division daughter-colonies; at 

 certain times sexual cells appear, the androgonidia and gynogonidia, 

 which retire to the center of the colony where 

 the latter are fertilized by the former and 

 after a resting period the zygotes develop into 

 new colonies: several species; in all parts of 

 the world. 



V. globator L. (Fig. 53). Colony of 1,500 to 



22.000 cells and up to 1.2 mm. in diameter; pro- 

 Fig. 53 Volvox 

 toplasmic threads may contain chromatophores : globator 



cosmopolitan. 



V. aureus Ehrenberg (V. minor Stein). Colony of 200 to 4,000 

 cells and up to .85 mm. in diameter; protoplasmic threads contain no 

 chromatophores : cosmopolitan. 



SUBCLASS 2. DINOFLAGELLIDIA.t 



Flagellates in most cases with a shell, around the equator of which 

 is a transverse groove in which lies a flagellum; a second flagellum is 

 also in most cases present, which may spring from a second and vertical 

 groove; body sometimes colored by chromatophores: 3 orders. 



Key to the orders of Dinoftagellidia here described : 



a t No transverse groove ; 2 flagella at forward end 1. ADINIDA 



o a Two grooves, a transverse and a longitudinal 2. DINIFERIDA 



ORDER 1. ADINIDA. 



Body without groove; 2 flagella at the forward end; shell composed 

 of a right and a left half: 2 genera. 



1. EXUVIELLA Cienkowsky. Body ovoid, shells compressed and 

 composed of right and left valves; 2 brown chromatophores present: 5 

 species; marine. 



* See "New Forms of Volvox," by J. H. Powers, Trans. Am. Mic. Soc., Vol. 27, 

 p. 123. "Light Reactions in Lower Organisms II Volvox," by S. O. Mast, Jour. 

 Comp. Neur. and Psy., Vol. 17, p. 99, 1907. "Le Volvox," by C. Janet, 1912. 



t See "New Species of Dinoflagellates," by C. A. Kofoid, Bull. Mus. Com. Zool., 

 Vol. 50, p. 163, 1907. "Dinoflagellata of the San Diego Region," by same, Univ. of 

 Cal. Pub. Zool., Vol. 3, p. 299, 1907. 



