REVIEWS AND BOOK NOTICES. 45 
mollusk is concentrated or sac-like; hence the term Saccata 
applied to them by Professor Hyatt. 
In the mollusk the viscera are usually contained in a large 
chamber protruding above the foot, while in the worm ‘‘ the sym- 
metry of the body is never disturbed by the — 
viscera.” In the mollusk, moreover, the man- 
tle is sac-like, ‘‘inclosing a conspicuous cav- 
ity,” and protecting the gills, while the ali- 
mentary canal is straight in the worm, rarely 
convoluted, and suspended freely in the peri- m 
visceral cavity, by bands (Fig. 1, b); in the 
mollusk this organ is always sandali, and & 
intimately blended, or united, with other or- 
gans. The nervous system of the worms con- 
sists of a nerve collar from which start two 
parallel chains of ganglia,while in the mollusks foot; b - ays m, mouth; : rf 
there is a nerve collar, but no double chain, gill 
and instead, nerves are thrown out to the sensory, motor and 
parieto-splanchnic regions. The eggs of worms are usually (ex- 
cept in the leeches) set free in the general cavity of the body, 
which is not the case with the mollusks. Lastly, the embryo 
mollusk (Fig. 6) early develops a shell composed of one or two 
pieces, while the embryonic worm is usually distinctly ringed, 
as seen on the opposite page. 
Here, in passing, we would remark that while the mollusks are 
admirably characterized, the author has, we think, failed to give 
sufficient importance to the most fundamental and important char- 
acter in the typical worm. Certainly the ringed, segmented 
structure of the worm is that which, more than any other char- 
acter, separates it from other animals, and when the rings are 
absent, as in the Planarians, Nematoids and other low worms, this 
is an adaptive character resulting from their peculiar habits. 
Moreover it should be remembered that our author regards the 
Brachiopods as a division of Chatopod worms, in which the seg- 
ments are invariably present, and form the most important feature 
of those animals. Again, we fail to find any reference to the re- 
lation of the most important anatomical systems (the nervous, cir- 
culatory system and digestive canal) to the walls of the body. e 
correlation in structure of the nervous system of the higher worms 
to the segmented structure is also most intimate and remarkable. 
Fig. 6. 
s 
Embryo yt vexed apa 
