THE HJIMOFLAGELLATES. 273 



essentially comparable in mauuer and origin to gregarinoid 

 or eugleuoid movement, would naturally lead us to expect 

 that the sensitive or anterior extremity goes first. The fact, 

 therefore, that this mode of progression is with the non- 

 flagellate end in front in all the instances hitherto recorded, is 

 of considerable importance in the present argument. It 

 entirely negatives — in the writer's opinion it distinctly out- 

 weighs — the opposing fact that the movement during rapid 

 displacement usually occurs with the flagellate end leading. 

 For, in these energetic movements, where the principal object 

 of the parasite is to change its vicinity as quickly as may be, 

 it obviously cannot much matter which end goes first, the 

 determining factor being, doubtless, mechanical considera- 

 tions (cf. also the account of movement). 



As a corollary may be mentioned the plastic or '^amoeboid" 

 nature of the non-Hagellate end in Trypanosoma — i.e. its 

 power of retraction and extension, commented upon by 

 Laveran and Mesnil (cf. fig. 42 d, of T. equiperdum). In 

 short, all the physiological data we possess tend to show that 

 this non-flagellate end in Trypanosoma is the sensitive ex- 

 tremity, and homologous with the anterior end of Herpeto- 

 monas, Trypanomorpha, and Trypanoplasma. 



(6) Morphological Points. — Reference has above been 

 made to the frequent presence of a vacuole near the uon- 

 Hagellate end in different species of Trypanosoma (e.g. T. 

 brucii, T. gambiense, Hanna's Trypanosoma of Indian 

 birds, etc.), here considered to be a normal cell-constituent 

 (though not necessarily one of invariable occurrence), which 

 probably represents the (originally) contractile vacuole of 

 an ancestral H^moflageliate. For there is no reason to 

 doubt that this vacuole is homologous with that described 

 both in Trypanoplasma (fig. 17 i'} and in certain Herpeto- 

 mouadine forms. ^ The important point of distmction is that 



' In Trypanomorpha, it will be remembered, Scbaudinn describes 

 one or more cytoplasmic vacuoles of varying size, in the anterior part 

 of the body (cf. fig. 8) ; this perhaps represents a more advanced condition, 

 iu which the formation of a distinctive organella is tending to be lost. 



