306 REVIEWS. 
the proper support of an individual it is evidently necessary that 
ae pato whether microscopical in size or not, should be obstructed in its 
ve in p 
a creature in which all this is reversed, and a digestive system is presented 
to us which is dioc aqu) increasing its facilities for getting rid of food 
as fast as it is swallow ow this reversal of the animal economy can 
be of service to the race we cannot see, so long as we regard the ies 
as an individual, or an aggregation of large individuals; but if on the 
other hand we adopt the opinion of his opponents, then all these ant 
ties disappear. We then see that the pores act as a strainer admittin ng 
only bodies of small size, such as are appropriate for the sustenance of 
the monads, which cover the internal surfaces of the canals. The e grad- 
ual tede sn of these canals into a central trunk becomes at once ap- 
propriate, when we compare it with the similar facilities which are found: 
in al Mn: communities for ism the colony of refuse and 
deleterious matters. The fact noticed by author, with m arked em- 
ith 
lade Soros is also explained, and the vase-like form of these cells 
noticed by Carter, and the amoeba-like d of the external mem- 
brane, accords spony well with this view. We do not find in this article 
upon a question of fact as regards the structure of the single cells of the 
internal membrane we may look for an early solution of this vexed ques- 
tion. 
If we dropped the review here it would be treating aea SEA 
with great injustice. Though forced to criticise the main point of his 
h 
other works of this eminent German zoologist, will "i bargs felt in the 
history of the progress of knowledge in this departm 
The account of the function and structure of the orit and of t 
inne of the ** ova" from special forms of his so-called cells of i^ 
int 1 membrane are of the greatest interest and importance. That, 
also, of ine gradual development of the canal system gives us an entirely 
new and original view of sponge structure. In this connection the re- 
a 
however to coalesce again as they approach maturity and uni ari- 
ous apertures into one viec trunk and single aperture; and also, that 
we can trace the origin of a species from common stem form 
To 
ilustrate this last scel the author instances two species, Guancha 
blanca and Sycometra compressa, whose variations are so great, and indi- 
