144 



Chlorophycece 



which has attained a maximum state of specialization in the 

 direction of an increase in the complexity of morphological 

 characters, accompanied by degeneration of sexual differences. 



ANCESTRAL FILAMENTOUS CONJUGATES 



Gonatozygon 

 GONATOZYG^E 



Cylindrocystis 



SACCODERM^E 



Ichthyocercus 



___ 

 / Triploceras Euastrum ' "">r " V 



Penium \ 



-IV 



'C^JPenium LiboTluhf^V" ^ 



x. / S I * Roya > 



Tetmemorus -y I / 



Closterium .' 



CLOSTERIE^E 



Docidium 

 Pleurotsenium \ 



Cosmarium 



Micrasterias 



Xanthidium 

 Staurastrum 



y .." 'SpondyL 



\ / Hyalotheca 



\ '. ^ 



Arthrodesmus 



\ 

 COSMARIEJS 



Onychonema ". 



Sphaerozosma _./ 

 \ ', Phymatodoois - Li;'lll . _ . j 



\ .**' Streptonema . 



x .^ 4: 



^ . Desmidium / 



x ^ ./ (Didymopriutn) 



^"^ ' 1 ' 



-. / ft 'f / 



<. __ Gymnozyga ^, 



Phylogeny of the Genera of Desmids. 



There is little question that this complexity of outline, which is so 

 frequently accompanied by a defensive armour of spines and spinous 

 processes, has been acquired as a means of defence against the 





