674 REPORT— 1881. 



Inside the fine groove, wliich in life can, no doubt, he opened and expanded, a 

 longitudinal ridge is situated, which is coated witli cilia, protrusible in its tiu'n, 

 and most probably the homologue of the foot in otlier Mollusca. 



On touching the exterior surface of tlie animal it feels rough and stiff; this is 

 caused by innumerable small spiculse in its integument, which are intermixed, in 

 a more or less regular arrangement, and several layers of which are superposed one 

 upon the other. They are calcareous, supported by and formed in a sort of cellular 

 cup surrounding the base, which remains in communication with the deeper cellular 

 layers of the integument. Between them a homogeneous chitin-like substance is 

 present, holding them in their places. 



Similar structures may be noticed in the. integument of Chiton on the sloping 

 sides of tlie mantle laterally with the dorsal plates, and these structm-es are, perhaps, 

 more marked in young than they are in older stages. 



In Chitonellus, where the dorsal plates are considerably reduced, tliey were 

 found in a much greater number by a German searcher, several years ago. Similar 

 calcareous spicules, differently arranged and shaped, however, are present in Chseto- 

 derma and Neomenia. 



With reference to the digestive canal, which is wholly symmetrical, I Lave little to 

 remark. It is internally provided with deep folds, and part of it is strongly ciliated, 

 in both respects closely resembling Neomenia. Neither coidd a separate liver be 

 detected, special secreting cells in the walls of the intestine apparently supplementing 

 the functions of this organ. Internally the mouth is surrounded by circular or semi- 

 circidar folds of the pharyngeal epithelium ; one of these is provided with numerous 

 nerve -branches running towards it, and must be looked upon as a sort of circular 

 lip. Over the muscidar buccal mass a curious blind prolongation of the posterior 

 thin-walled portion of the intestine takes its coiu-se ; this terminates anteriorly 

 in- the head. Posteriorly on the floor of the buccal mass a small slit-like opening 

 is found, leading into a median cavity containing the radida and into two lateral 

 tubes, the salivary glands. As Neomenia is entirely deprived of a radula, and was 

 for this reason removed from the MoUusks, it is important to notice that its close 

 ally, Proneomenia, is possessed of one. It is also a very suggestive fact that the radula 

 of this latter form, though perfect and complicated in shape, is so extremely 

 diminished in size thatjt may be said to be degenerate and on its way to be lost, 

 a stage which has been reached in Neomenia. For this reason the apparently less 

 diflerentiated Neomenia may not be looked upon as the more primitive ; the im- 

 portant ancestral character which it has lost is, however, retained in its ally, and 

 this induced me to choose the name of Proneomenia for the latter. 



In passing on to the nervous sj-stem, always so important in classification, 

 a general remark may be made respecting a more primitive characteristic of the 

 uei-ve-tissue of this animal. Although both ganglia and nerve-stems are present, 

 .still the latter are everywhere accompanied by nerve-cells, which in the ganglia 

 are more numerous. 



The brain is situated close to the front termination of the body, and three 

 principal pairs of nerves originate from it, one pair forming the sublingual ring, the 

 others being continued in the longitudinal pedal and longitudinal lateral stems. The 

 two pedal nerves are united by transverse commissures, such as were noted for 

 Chiton and Neomenia. In Chiton this was inadequately intei-preted as an approach 

 to what is called in German the StricMeiterne7-ven-system of segmented invertebrates. 

 Traces of it were found in such lower Mollusks as Haliotis and Fissurella ; its 

 increased complication in the Amphinem-a nevertheless shows it to be of importance 

 in determining the phylogenetic affinities of these animals. Moreover Proneomenia 

 in another important character shows a greater complication, viz. ia the presence 

 of a system of transverse commissures between the lateral and the pedal stems. As 

 numerous finer branches spring from these transverse commissures, as well as from the 

 longitudinal stems, a gradual approach is here noticeable towards that form of nenous 

 >iystem which has been described by Lang for marine flatworms, in which a dendritic 

 and general anastomose of commissures in the most different directions is present, 

 and further on to a still more primitive stage, in which even the meshes between 

 this network of nervous tissue are filled up, and in which a continuous plexus of 



