1914] Sharp: Diplodinium ecaudatum .73 



zone, which is locomotor only in function, and an acloral locomotor 

 apparatus or adoral membranelle zone, which is both locomotor and 

 nutritive in function. Considered from the point of view of its 

 probable evolution, this adoral row of membranelles was undoubtedly 

 primarily nutritive in function, but owing- to developmental changes 

 which have probably taken place, combined with the increasing neces- 

 sity of greater speed or possibly the decreasing necessity of food- 

 getting, this nutritive function has gradually been given over to that 

 of locomotion, so that at the present time the function of this adoral 

 row of membranelles may be regarded as primarily locomotor and 

 secondarily nutritive. This conclusion has been reached after due 

 consideration of the morphological position of the adoral membranelles 

 combined with careful observations made of the living, active animals. 

 Such observations invariably lead one to the conclusion that the adoral 

 row of membranelles functions mainly as an organ of locomotion. 

 And in this connection it is interesting to note that, of all the different 

 species of the genus Diplodinium, the species ecaudatum is provided 

 with the most powerful and the most complicated organs of locomotion. 



Dorsal locomotor apparatus. — The dorsal locomotor apparatus, or 

 dorsal membranelle zone, is placed transversely at the very anterior 

 extremity of the dorsal surface of the body and consists of an outer 

 and inner dorsal lip (o. d. lip and i. d. lip, figs. B, C ; pi. 4, figs. 3-4), 

 an outer and inner dorsal furrow (o. d. fur. and i. d. fur., figs. B, C ; 

 pi. 4, figs 3, 4), and a row of twenty-six membranelles {d. m., figs. B, C ; 

 pi. 4, figs. 3, 4; pi. 7, figs. 23-25). 



Beginning at a point just dorsal to and slightly posterior to the 

 dorsal extremity of the base of the left skeletal area {I. sk. a., pi. 3, fig. 

 2) the dorsal row of membranelles extends transversely around the 

 anterior extremity of the dorsal surface to the right side, where it 

 makes a short curve anteriorly to end just dorsal to the dorsal ex- 

 tremity of the base of the right skeletal area (r. sk. a., pi. 3, fig. 1 ; pi. 

 4, fig. 4) . The bases of these membranelles extend down into an inner 

 dorsal furrow {i. d. fur., fig. B) and are there enclosed by a fold 

 of the ectoplasm and cuticle which in cross-section resembles the 

 human lower lip and has therefore been designated as the inner dorsal 

 lip (^. d. lip, fig. B; pi. 4, figs. 3, 4). Outside of the inner dorsal lip 

 is a second fold of ectoplasm and cuticle, not so high as the inner lip 

 but much thicker and more substantial. This outer fold also resembles 

 a lip and is therefore termed the outer dorsal lip (o. d. lip, fig. B ; pi. 4, 

 figs. 3, 4). The outer surface of the outer dorsal lip is continuous 



