CHAPTER XXIX. 



AMPHINEURA.* 



Systematic :- 



A. SOLENOGASTRES. 



Neomenia, Proneomenia, Dondersia, Chaetoderma. 



B. Chitones. 

 Chiton. 



The Amphineura appear to be the most primitive of all living 

 Mollusca ; this is especially evident when we consider such a form 

 as Proneomenia, with its long, almost cylindrical body strongly re- 

 sembling that of a worm, and even capable of worm-like movements 

 (Fig. 147), a further resemblance being found in the complete 

 absence of that most characteristic Molluscan structure, the shell 

 (not even an embryonic shell-rudiment being present). Unfoi'tunately, 

 the ontogeny of these very forms, which we are inclined to regard as 

 the most primitive, is but little known, and Avhat we do know con- 

 cerning the ontogeny of the Amphineura is but little understood. 

 That of Chiton has so far been the best investigated (Loven, Kow- 

 alevsky, Metcalf) and a little has also been recently made known 

 of the development of Dondersia {Myzomenia), one of the Solenogastres 

 (Pruvot, Nos. 13 and III.). 



Since the development of Chiton has been studied in greater detail 

 than that of Dondersia, it will be convenient to commence our study 

 with the former and refer back to it when dealing with the ontogeny 

 of the Solenogastres.j- 



* Mollusca. I. Amphineura. II. Lamellibranchia. III. Solenoconcha. 

 IV. Gastropoda. V. Cephalopoda. The arrangement of these divisions of 

 the Mollusca and their inter-relationships will be discussed in Chapter xxx. 



t [Sedgwick (Text-Book of Zoology, 1898) expresses the opinion that the 

 class Amphineura is quite unjustifiable: for whereas the Chitones are un- 

 doubted Gastropods, he considers it by no means certain that the Soleno- 



B 



