LITERATURE OF THE AMPHINEURA 63 



ganglionic swelling. A small perirectal commissure originates 

 from this swelling. The pedal cords are united with one another 

 and with the pallial cords of the same side by anastomoses in the 

 anterior region of the body. A small stomato-gastric commissure, 

 bearing two small stomato-gastric ganglia on the middle of its 

 course, arises from the cerebral ganglia and surrounds the 

 oesophagus. There are no organs of special sense except a dorsal 

 posterior and median pit, corresponding to the precloacal fossa of 

 the Neomeniomorpha. 



The sexes are separate. The azygos gonad occupies the same 

 position as the paired gonads of the Neomeniomorpha, and com- 

 municates by a median aperture Avith the pericardial cavity. The 

 generative products are conducted from the pericardium to the 

 exterior by the renal ducts. The embryology of the group is quite 

 unknown. 



The Chaetodermomorpha are marine animals feeding on lowly- 

 organised forms of life, such as Protozoa, etc. They are found in 

 oozy bottoms from a depth of 15 fathoms to abyssal regions. 

 The nine recorded species of the single genus Chaetoderma come 

 from the North Atlantic, North Pacific, and Arctic Oceans, the Sea 

 of Marmora, the Eastern Archipelago, and the Philippine Islands. 



Family CHAETODERMATIDAE, von Jhering. Genus Chaetoderma, 

 Loven. The characters are those of the sub-order. Limifossor, Heath 



(Alaska). 



PHYLOGENY OF THE AMPHINEURA. 



The Polyplacophora present the most archaic characters among 

 the Amphineura. The Aplacophora, on the other hand, are 

 specialised in the following respects : (1) in the great reduction of 

 the foot ; (2) the disappearance of the shell (Cryptoplax, among the 

 Polyplacophora, shows how these two reductions may take place 

 simultaneously) ; (3) the absence of the radula in several forms. 

 The Chaetodermomorpha seem to be more specialised in these 

 points than the Neomeniomorpha. 



LITERATURE OF THE AMPHINEURA. 

 I. Polyplacophora. 



1. van Bcmmclen. Zur Anatomie der Chitonen. Zool. Anzeiger, 1883, p. 340. 

 2. Blumrich. Das Integument der Chitonen. Zeitschr. f. wiss. Zool. lii. 

 1891, p. 404. 



3. Burne. Notes on the Anatomy of Hanleya Hanleyi, M. Sars. Proc. 



Malacol. Soc. ii. 1896, p. 4. 



4. Garnault. Sur la structure et le developpement de 1'ceuf et de son follicule 



chez les Chitonides. Arch. Zool. Exper. (2), vi. 1888. 



5. Haddon. On the Generative and Urinary Ducts in Chitons. Proc. R. 



Dublin Soc. new ser. iv. 1885. 



