60 
2) by the multiple layer of spieules in the integument; 
3) by the absence of branchiae in the posterior extremity (pre- 
sent in C'haetoderma); 
4) by the absence of special male generative ducts, ete. (penis, 
penis-sheath, vas deferens, receptaculum seminis) ; 
Chaetoderma is finally especially distinguished: 
1) by the details of its nervous system; 
2) by those of its digestive apparatus, in which a special co- 
cum-like appendage, representing a very primitive liver, 
develops. 
The close relationship between the three genera of Soleno- 
gastres is sufliciently demonstrated by the comparison above given. 
That between the two orders of the elass of the AMPHINEURA, the 
Solenogastresand the Polyplacophora,is much less close. The 
Chitons (Chiton, Chitonellus, Cryptochiton, ete) which belong to 
the last named order represent a stage which is more differentiated 
in several directions. The following scheme may to a certain de- 
gree represent the affinities between the two orders. 
1) In both orders calcareous spieules are developed in the integu- 
2 
3 
4 
) 
) 
DZ 
ınent: in the Polyplacophora they are specially numerous 
in the young stages. Their shape and mode of growth also 
offers points of comparison. 
The type of the nervous system corresponds to the same 
groundplan, even in detail. 
In both orders a very complete bilateral symmetry obtains, 
internally as well as externally. 
In both orders there is a tendency towards metamerie sub- 
division. In the order of the Polyplacophora this is ob- 
serveable in the dorsal shields, in the nervous commissures 
and even in the shape of the body of the larva. In the fa- 
mily of the Neomenindae similarly in the nervous system, in 
the genital gland, in the slanting transverse muscular bundles 
between the intestinal folds and perhaps in the intestinal folds 
themselves. In Chaetoderma no observations on this head are 
as yet on record. 
