62 SYNOPTIC COLLECTION. 



spheres leave the parent one by one, rotating swiftly 

 through the water. 



After asexual reproduction has continued for some 

 time, cells which are apparently parthenogonidia at first 

 become biflagellate male cells or microgonidia (fig. 4) . 

 and large, unflagellate female cells or macrogonidia ; 

 one of these macrogonidia (fig. 5) is being fertilized by 

 the microgonidia. This process of fertilization is similar 

 to that of specialized plants and animals ; after fertiliza- 

 tion, cleavage takes place and both somatic cells and par- 

 thenogonidia are formed before the embryo leaves the 

 parent. After this, the young develops into a sexual 

 adult (fig. 6). In this figure, a is a male cell seen from 

 above ; a 2 the same from the side ; a 8 with the micro- 

 gonidia separated ; a 4 with only a few microgonidia ; the 

 others having escaped are moving about in the central 

 cavity. Fig. 6 b, is a female cell ; b 2 the same with 

 vacuoles in the inside ; in b 8 the microgonidia have fast- 

 ened themselves on the gelatinous covering of the female 

 cell ; sometimes three penetrate the covering and bore 

 into the interior, when a fertilized egg results, which is 

 the sexual method of reproduction in Volvox. 



The extremely interesting observation of Ryder 1 on 

 Volvox minor shows, that, in spite of its nearly spherical 

 form, there is a polar differentiation of the body with the 

 specialization of possible sense organs at the anterior pole. 

 According to this investigator the anterior pole of the 

 blastula is always directed forward when the animal is in 

 motion, and therefore it is this pole which is brought into 

 the most dangerous position. Now, it is instructive to 

 note that the peculiar organs known as " eye-spots " are 

 developed much more at this pole than elsewhere, being r 

 in fact, so slightly developed at the posterior pole, where 

 there is little use for them, as to be nearly absent. There- 



1 Amer. Nat., XXIII, 1889, p. 218-221 ; also Proc. Acad. Nat. 

 Sci. Phila., May, 1889, p. 138-140. 



