128 



THE PROTOZOA 



forms the complete colony ; or the zygote may first divide into 

 two or three individuals, each of which forms a sixteen-cell colony. 

 Pringsheim ('69) stated that a dimorphism exists in the gametes 

 formed by large colonies and by small ones, and maintained that 

 the larger gametes never conjugate amongst themselves, while the 

 smaller ones can unite with each other or with the larger ones 

 (Fig. 126). 



An incipient sexual difference in the colony is thus indicated, 

 although, as in chlamydomonads, the size difference in gametes 

 is apparently facultative. The sexual difference is somewhat 

 better marked in the genus Eudorina, although the most reliable 

 authorities differ as to the details. According to Goroschankin ('76) 

 and Dangeard ('89), the sexually mature colonies are easily distin- 

 guished as male and female, the latter resembling the ordinary colo- 

 nies save for a slightly 

 larger size. The male 

 colonies are at first 

 quite similar to the 

 ordinary colony, but 

 each of the sixteen cells 

 divides to form a six- 

 teen or thirty-two celled 

 plate, and each of 

 these cells gradually 

 becomes long and 

 spindle-formed and de- 

 velops flagella at the 

 pointed end. They 

 ultimately become free 

 and unite with larger 

 ovoid cells. Carter's ('58) description differs so much from this 

 that Butschli doubts if he had the same species. He found that 

 the colonies are hermaphrodite and divided into male and female por- 

 tions. Four cells at one pole of the oval colony develop into sperma- 

 tozoids, while the remaining twenty-eight cells become enlarged, and 

 as ovoid cells, are probably fertilized by the spermatozoids. These 

 observations, although conflicting, at least show the increasing com- 

 plexity of the colony, and a differentiation, according to Carter, of 

 male and female cells in the same multicellular individual, or accord- 

 ing to Goroschankin, the colonies of Eudorina, become multicellular 

 individuals in which the sex is definitely established. In these cases 

 there is no distinction between germ and somatic cells, all being 

 capable of assuming the plasmatic condition necessary for conju- 

 gation. 



-Conjugation of Pandorina morum Ehr. 

 [Pringsheim.] 

 Large gametes conjugate with small ones (/?, C), or small 

 ones conjugate with each other (D, E, F). The result is always 

 a zygote ( G) . 



