300 ALG^ 



consists simply of a single motile primordial cell, in other words, of a 

 zoospore or swarm-cell. These are megazoospores, half as long again 

 as broad, each with two contractile vacuoles, a lateral red pigment-spot, 

 and two long cilia ; in the posterior half is a nucleus. After the con- 

 clusion of the period of swarming, these zoospores become invested 

 with cellulose, and, after a long period of rest as hypnospores, multiply 

 non-sexually by division into four — less often into two. According to 

 Rostafinski sexual reproduction takes place by one of these mega- 

 zoospores dividing, by successive bipartitions, into eight daughter-cells, 

 which are then microzoospores — or, more correctly, zoogametes. These 

 have a longish almost elliptical form, and a light green colour, one 

 nucleus, a red pigment-spot, and four cilia. They are distinguished 

 from the true zoospores, not only by their smaller size, but also by the 

 large colourless extremity in place of the two contractile vacuoles. They 

 swarm out, and soon begin to conjugate in pairs, coming into contact 

 by their colourless extremities, and coalescing into a single cell, the 

 ends which bear the cilia at the same time rounding off and approxi- 

 mating. This body has now eight cilia and two lateral pigment-spots ; 

 ultimately the eight cilia disappear, and a zygosperm is formed, which 

 multiplies by simple division without swarming. Dangeard finds in 

 Chlamydomonas pulvisculus (Miill.) a differentiation of male and female 

 gametes, the latter being considerably larger than the former. In C. 

 Morieri (Dang.) he describes a peculiar mode of conjugation of zooga- 

 metes, which he compares to that of Spirogyra. 



Chlamydococcus A. Br. presents a similar life-history ; and, according 

 to some observers, the organisms known as Pleurococcus, Gloeocystis, 

 and others usually included under Protococcaceas, are identical with the 

 resting conditions of Chlamydomonas ; and, under suitable conditions, 

 can be made to produce biciliated zoospores with two contractile 

 vacuoles and a nucleus. 



Under the Volvocineae, and near to Chlamydomonas, Dangeard 

 {Ann. Sc. Nat., vii., 1888, p. 105) and Stein include also Chlorogonium 

 <Ehrb.). 



Among the most interesting of the social Pandorinese is Pandorina 

 Ehrb.. Each family or ccenobe consists of sixteen cells closely crowded 

 together, and surrounded by a thin gelatinous envelope through which 

 the cilia protrude. Non-sexual multiplication is preceded, after the 

 colony has come to rest, by the absorption of the cilia in the sixteen 

 cells, each of which then breaks up into sixteen smaller cells ; and these 

 sixteen daughter-families are set free by the absorption of the gelatinous 

 envelope of the parent-colony; each becomes itself invested by a 

 gelatinous envelope, and grows to the size of the original parent-colony, 



