144 



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 



Genicularia \ 



Gonatozygon 



I 

 t 



V GONATOZYG.E 

 \ 



N 



SACCODERM^E 



Ichthyocercus 



Tetmemorus\ I 



/ ^-" ''"' "Lx^ r +S? Closterium / 



*f^ j-, if [Penium romutum] 



/ Triploceras Euaatrui ^ \. r,\.Q<Q,1VW&fc /' 



Docidium \ v ^___- f 

 Pleurotaenium \ 



J 



1 ' 

 I 



. ; Cosmocladium ; 

 Oocardiuro 



> .' 'Spondylosium 



V ;' / Hyalotheca 



\ '. ^ 



Onyclionema 

 Sph;erozosma 



/ 



'. Phymatodocis ii:lll. __. , / 



\ .*** Streptonema . 



4; . 



. Desmidium / 



^^ / (Didymopn, / pLACODEBBLB 



^ ~^ __ Gymnozyga x / 



Phytogeny 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 



