VOLVOCINE-cE. 69 



from other zoospores. At their colourless apex they exhibit, like 

 other zoospores, a red body placed on one side of the apex, and two 

 long vibrating cilia, by which they move in the manner common to 

 zoospores. The individual zoospores exhibit no marked differences, 

 except that they vary in size within tolerably wide limits, but not in a 

 manner to indicate the existence of two different sorts. 



Amongst the groups of isolated zoospores of different sizes some are 

 at last seen to approach one another in pairs. They come into 

 contact at their anterior hyaline apex, coalesce with one another, and 

 assume a shape resembling a figure of 8. The constriction which 

 marks their original separation disappears by degrees ; and the paired 

 zoospores form at last a single large green globe, showing at the cir- 

 cumference no trace of their original separation. It may be seen, 

 however, that the globe is larger than the individual neighbouring zoo- 

 spores, that it has a strikingly enlarged colourless mouth spot, with 

 two red bodies on the right and left, and that it is furnished with four 

 vibrating cilia originating in pairs near the two red spots. The four 

 cilia, however, soon become motionless, and together with the red spots 

 disappear. 



This act of conjugation occupies some minutes from the first contact 

 of the zoospores to the formation of the green globe. The latter 

 becomes the oospore, which, after growing slightly larger, and assuming 

 a red colour, germinates after a long period of rest, and brings forth a 

 new Pandorina. There is hardly any appreciable difference, except in 

 size, between the male and female zoospores. Most frequently a small 

 zoospore pairs with a larger one ; but two of equal size often unite. 

 Probably both the females and the males vary much in size, the former 

 more so than the latter. 



With regard to the entire plants from which the zoospores are pro- 

 duced, there is little doubt that those of the largest size are females ; 

 but the sex of the smaller and middle-sized ones cannot be determined 

 with any certainty. The germination of the oospore is like that of other 

 Volvocinete, especially resembling in its early stage the germination of 

 the resting spores produced by the microgonidia of Hydrodictyon utri- 

 culatiim. The oospore bursts, and produces a single large zoospore (in 

 rare cases two or even three), which divides into sixteen cells, and 

 becomes a young Pandorina. 



Plate XXVII. fig. 2. Pandorina morum a, a very small family ; 6, 

 c, sixteen-celled families ; d, eight-celled family ; e, solitary cell ; /, the 

 same, further magnified, showing process of subdivision ; g, 32-celled 

 family ; h, small family undergoing division ; i, 16-celled family 

 divided into sixteen daughter families. All after Stein X about 500. 



GENUS 42. GONIUM. Mutter. (1873.) 



Coenobinin quadrangular, tabular, angles rounded, formed 

 from a single flat stratum of cells, girt by a broad hyaline 

 plano-convex tegument. Cells 16 (central 4, periplierical 12 J, 

 polygonal, bright green, becoming with age disordered, granu- 

 lose, connected by the produced angles, chlorophyllose vesicle 

 central, furnished with colourless contractile vacuoles, and two 

 long exserted cilia. 



Propagation by repeated division of the cytioplasni. 



