298 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Chitonidae.* — Prof. L. II. Plate has published the first part of a 
memoir on the Anatomy and Physiology of the Chitonidae, based on 
his Chilian collection. He has been able, on some of the larger forms, 
to clear up certain points concerning the excretory and circulatory 
systems, which are difficult to study in the European species. The 
comparative and phylogenetic considerations are to be discussed in a 
general part; the present publication includes the first half of the 
special part, and deals with the two families Toniciinae and Liolo- 
phurinae. The gigantic Acanthopleura echinata is described in special 
detail. 
S. Lamellibranchiata. 
Phylogeny of Lamellibranchs.f — H. Douville adopts Neumayr’s 
classification : — Taxodonts, Dysodonts, Desmodonts, Heterodonts, and 
the imperfectly known Cryptodonts, an arrangement based essentially 
on the structure of the cardinal apparatus. He maintains that the 
Taxodonts represent the primitive source from which the Heterodonts 
are derived by simplification of the hinge and acceleration of develop- 
ment ; that the Dysodonts are Taxodonts progressively modified by their 
byssal fixation ; and that the Desmodonts are Heterodonts originally 
transformed by imprisonment within the cavity which they excavate. 
Yoldia.J — Mr. Gilman A. Drew gives an account of the development, 
structure, and habits of Yoldia limatiila Say, a member of Pelseneer’s 
order Protobranchia. 
The chocolate-brown eggs are laid free in the water ; cleavage results 
in sub-equal blastomeres; an epibolic gastrula is formed. Some of 
the ectoderm-cells wander into the interior, the endoderm-cells divide, 
and at one side of the resulting cell-mass a narrow tube appears, which 
opens to the exterior through the blastopore. As it has not been deter- 
mined whether this tube is ectodermic or endodermic, it may be called 
the ventral tube. About 42 of the ectoderm-cells become ciliated test- 
cells, and inside this a new ectoderm is formed. Some ectoderm-cells 
form the shell-gland, which is never a distinct invagination. The mid- 
gut is formed, as it were, as a continuation of the anterior end of the 
ventral tube. Two thick- walled ectodermic pouches are formed an- 
teriorly, as the rudiments of the cerebral ganglia, and the other ganglia 
soon appear. An anus breaks through into the upper part of the blasto- 
pore. At about the age of 105 hours, the embryo stops swimming and 
settles to the bottom ; the cilia shrivel, the test-cells break up, the 
animal is left in its clear white shell. The most striking peculiarities 
arc connected with the formation and disappearance of the locomotor 
test, which resembles that in Dondersia , but is otherwise unique. The 
condition presented by the mouth and anus both opening through the 
blastopore, and the formation of cerebral ganglia from invaginations, 
are also of much interest. The sensitive burrowing foot, the food- 
collecting palp-appendages, the muscular membranes suspending the 
gills from the body-wall, and other features of interest, are briefly 
described. 
* Fauna Chilensis. Supplementheft iv. Zool. Jahrb., 1897, pp. 1-243 (12 pis. 
and 8 figs.). f Comptes Rendus, exxvi. (1898) pp. 916-9. 
t Ann. Nat. Hist., i. (7 tli series) 1898, pp. 267-77 (6 figs.). Johns Hopkins 
Univ. Circ., Nov. 1837, pp. 11-14 (6 figs.). 
