PROTOPHYTA 



55 



is impossible. Reproduction occurs by division after the flagella 

 have been withdrawn. Unlike animal flagellates the volvox 

 group have a sexual phase in which gametes of equal size (iso- 

 gametes) are produced. These gametes are formed by the re- 



'.'o»o°?lfs'.'t 



"> Olo „?«».'»»<»«; 



Fig. 26— TYPES OF VOLVOX COLONIES 



.4, a quarter of a colony of Volvox globator. This species is hermaphrodite,* and eggs (r) and 



sperm cells (sp) are formed from cells which wander into the colony from the periphery (/>)• 



B, parthenogonidia-formingt colonies of Volvox aureus. C, female colony with unfertilized 



egg-cells. D, male colony with many bundles of spermatozoids 



From Oltmanns 

 Magnifications: A, 60; B, C, and D, 40 



peated divisions of an ordinary cell, and in consequence are 

 considerably smaller than the usual individuals resulting from 

 ordinary division.* 



Colony formation is highly developed in this group, the colo- 



* Hermaphrodite, an individual having both male and female reproductive 

 organs. 



t Parthenogonidium {plural, parthenogonidia), an individual which can pro- 

 duce a colony by one of the asexual methods — cell-division, spore-formation, 

 budding, etc., but does not include the self-fertilization of hermaphroditic 

 organisms. 



X In connection with this group it is interesting to note that the German botanist, 

 Adolf Pascher, was able (in 1916) to demonstrate a typical Mendelian inheritance 

 in these forms by crossing two different species of the related genus Chlamy- 

 domonas. This is the only case in which a typical Mendelian inheritance has been 

 demonstrated for an unicellular organism. 



