Ch Ian i ydon ion a-dese 



171 



wall with some other substance. The normal motile cells of Chlamydomonas 

 are equivalent to the zoogonidia of other Isokontse, and their characters are 

 sufficiently constant to furnish a basis for the discrimination of the various 

 species. The zoogonidia multiply rapidly by division which takes place 

 usually after the cell has come to rest. Two, four, or eight daughter-cells are 

 formed, the first division-plane being transverse, longitudinal, or oblique. 

 The daughter-cells quickly acquire the characters of the parent and are set 

 free by the conversion of the old mother-cell-wall into mucilage. 



Fig. 100. Chlamydomonas monuiiiiui Stein (~Chl. Linninii Gor. ). 13, fusion of hetero- 

 gametes; 46, palmella- states. Very highly magnified. (After Goroschankin, from Oltmanns.) 



All the species of Chlamydomonas can enter into a ' palmella-state,' in 

 which the cells lose their cilia, become enveloped in a copious jelly, and 

 undergo divisions of such a nature (often in oblique planes) that the mucila- 

 ginous colony extends in three directions of space (fig. 100 4 6 J ). There is 

 in this manner a great increase in the number of individuals, and when the 

 requisite combination of external factors once more supervenes they all 

 become motile and swim out of the jelly. This transitory palmella-state of 

 OMamydomonas is of great interest as it clearly indicates how the Palmel- 

 lacea i originated from the Chlamydomonadea? by an extension of the period 

 of quiescence and the gradual retention of a permanent gelatinous colony, the 

 zoogonidium-state having become of much less importance and only being 

 reverted to occasionally. 



