MORPHOLOGY AND TAXONOMY OF MASTIGOPHORA 289 



due to atrophy of the brain cells through lack of nutrition brought 

 about by collections of parasites and lymphocytes (Bruce). 



The Order Protomastigida includes a great variety of heterogen- 

 eous t^T^es of flagellates and is rather a catch-all of promiscuous 

 forms than a homogeneous and clearly defined group of Protozoa. 

 Flagella, for the most part, are limited in number to one or two, 

 but three are present in the bilaterally symmetrical Trimastigidse. 

 If two are present they may l)e equal in length (Amphimonadidse) in 

 which case no distinction can be made between primary and secon- 



Ji.. 



Fig. 138. — Protonionads. ^-1, B, Herpetoinonas musca-doniesticw; C, resting stage 

 of same;£), Crithidia subulata, nectomonad; E, resting forms of same; F, hapto- 

 monads of same attached to epithelial cell; (d) basal bodies; (k) parabasal body; (0 

 nucleus. (From Calkins after Prowazek and Leger.) 



dary flagella ; or, there may be a distinct difference between primary 

 and secondary (Monadidse, Bodonidse). The secondary flagellum 

 may be directed forward (Monas), laterally (Prowazekia) or back- 

 ward as a trailing flagellum (BodonidoB) or may be attached to the 

 periplast to form an undulating membrane (Cryptobiidce). The 

 single flagellum may arise from the anterior part of the cell (Bicoe- 

 cidse, Oicomonadida^, C'hoanoflagellida? and Phalansteriidse) or 

 with an undulating membrane from the posterior end (Tr^-pano- 

 somatidte). Protoplasmic collars surrounding the bases of the 

 flagella like the collar cells of sponges, are present in Choano- 

 19 



