38 QUATREFAGES, ON THE METAMORPHOSES 
of marine invertebrata, and such an investigation is found to 
be fatal to the cell-theory. Captivating and beautiful as the 
doctrine was, exceptional cases presented themselves at its 
outset which have now gradually increased and assumed pro- 
portions, which must compel us to reject it. ‘The comparison 
of the egg to a single cell does not now receive the unanimous 
support of physiologists, nor can it be allowed that all the 
corpuscles of the blood are in any way comparable to modified 
cells. M. de Quatrefages has shown that the most complete 
lobes of the vitelline structure in Hermella occasionally 
coalesce, and others have observed the same occurrences, 
proving that the supposed cell-wall, the vitellme membrane, 
is sometimes wanting. The non-cellular character of muscu- 
lar tissue is considered as beyond doubt, but it is the discovery 
and appreciation of that primitive, contractile, protemaceous 
substance, known as sarcode which seems to have dealt the 
heaviest blow to the cell-theory. The study of the structure 
and reproduction of many forms of Protozoa, has shown the 
existence of vitality apart from cellular structure and vast 
as may be the import and truth contained in Schwann’s 
theory, yet its universality can no longer be admitted. M. 
de Quatrefages has clearly stated the history of the cell- 
theory and whilst successfully combating its doctrines, main- 
tains its partial truth and the benefits that Schwann and 
Schleiden effected through it for science. 
Passing over the highly interesting chapters on the meta- 
morphoses of insects, and the no less interesting description 
of the author’s own researches on the larval forms of mollusca 
we arrive at that portion of the work devoted to the descrip- 
tion of the phenomena entitled by him geneagenesis. The his- 
tory of the whole subject and the gradual progress of discovery 
bearing upon this department of zoological science, up to the 
present time, are clearly and elegantly narrated by the author, 
the references to important original works, being not the least 
valuable part of these chapters. Previous to the year 1759 
the idea generally prevailed among naturalists that species 
could only be reproduced by the contact of two diverse ele- 
ments, germ and sperm, each seated in a different individual. 
The exceptional facts observed in the case of man himself and 
the fables of the ancients prepared our forefathers for the dis- 
covery of certain animals in which the sexes were united, 
and these were at length discovered in the lower classes of 
animals, the worms and slugs for example. 
Adanson’s researches at a later period impressed these 
facts more fully upon the minds of men of science, and 
gave rise to this problem; “Can any animal be a male and 
