380 



THE AMERICAN NATURALIST [Vol. XLIV 



with the Ciliata since the posterior circlet of cilia formed on the 

 bud of Acineta is a convergence phenomenon attendant upon the 

 free-swimming life of this stage rather than primarily an ances- 

 tral character indicating the derivation of the Suctoria from the 

 Ciliata. 



Again the occurrence of flagellate-like stages in the life his- 

 tory of the Plasmodium . Unix sin and L< ishma n in is not regarded 

 as of phylogenetic significance but as an independently derived 

 adaptive stage. The Haemosporidia are therefore not transferred 

 from the Sporozoa to the Flagellata by Doflein as Hartmann and 

 others have argued. On the other hand, the trypanosomes are 

 regarded as having been derived from parasites of insects such 

 as Herpetomonas and Crithidia, whose forms they resemble in 

 culture media. 



Doflein is skeptical about the specific distinctness of the vari- 

 ous pathogenic trypanosomes of mammals, thoimh recognizing the 

 necessity of distinguishing them to avoid confusion, by their 

 hosts, occurrence and typical form in the blood of the host. 

 They are forms merely, not fixed species, and doubtfully even 

 incipient species. He holds as uncertain even the specific dis- 

 tinctions in the so-called gametes of T. gambiense and T. brucei 

 in the tsetse fly reported bv Koch. He also rejects as hypothet- 

 ical the sexual cycle of T. lewin in the rat louse reported by 



However the more recent work of Minchin ^Baldry and Breinl 

 and Hindle tends to confirm the view that a sexual phase of the 

 parasite may occur in the insect host. 



The Protozoa are regarded as a group whose limits are arbi- 

 trarily defined in the interests of economy in scientific work 

 rather than by structure. No sharp boundary line separates 

 then on the one hand, from the Metazoa— witness the spore of 

 Xosema or that of the Act inomyxidia— or, on the other, from the 

 lower Metaphyta, as may be seen in the family Volvocida? within 

 which numerous types of colonial organization have been evolved. 

 Not only do the Protozoa intergrade with Metazoa, the lower 

 altra\ moulds and fungi in morphological characters, but also in 

 physiological as well. 



The author has for some years consistently maintained that the 

 lowest branch of the Protozoa is not the Rhizopoda as stated in 

 practically all text-books and manuals, but rattier that the Masti- 

 gophora are to be regarded as lowest in the scale of organization. 

 This is based not only upon the occurrence of flagellated forms 

 in the gametes or other reproductive phases in the life history of 



