1885.] Embryology. 317 
much as the Teleostean paired fins have been specialized and 
altered in the course of the history of the phylum. 
If it is, therefore, found difficult to trace the nerve supply of 
the pelvic fins which have been thus shifted into a jugular or tho- 
racic position to segments above them, or to reconcile their mode 
of innervation with the lateral-fold theory of their origin proposed 
by Balfour, the comparative anatomist who confines himself to the 
study of adult structures should not be surprised, for he can know 
nothing of the translocation of the whole fin-rudiment forward 
and downward unless he is acquainted with the process which 
brings this about. Neglecting this, he remains ignorant of what 
embryological investigation and investigators might do for him, 
though he will often criticise the conclusions of the latter upon 
the basis of his knowledge of adult structures, which, as in the 
case above instanced, would manifestly be insufficient to enable 
him to get at the truth. This interesting example of the value of 
embryological observations as the basis for deductions in scientific 
morphology, reminds the writer of what Bruch’ has said, to the 
effect that, “In the kingdom of nature, as in history, all that has 
become is to be understood only through its decoming.” 
Lophius is an extreme type, yet other equally interesting forms 
have been described, traced and figured by Mr. Agassiz; for ex- 
ample, Gadus does not bud out the rudiments of its pelvic fins so 
early as Lophius, though another form, Mallotus (= Onos), seems 
to bud out the pelvic limb nearly as soon as the embryo angler. 
Gadus is evidently intermediate —/John A. Ryder. 
DEVELOPMENT OF THE VIVIPAROUS EDIBLE OysTER.*—In this 
essay, the text being duplicated in Dutch and French, Dr. Horst 
brings together about all the information of value which has been 
acquired by his pfedecessors and contemporaries, and also gives 
an account of his own investigations, especially those which relate 
to the development of the shell-gland and gastrula, which he had, 
however, first published two years ago. The gastrula is the first 
shell-gland_ on nearly the opposite side of the blastula? The 
mouth is formed at the time of invagination of the gastrula; the 
anus is formed later, and is broken through at the end of the gas- 
trular pouch of endoblast, which blends with the ectoblast, which 
also becomes perforated where the two blend. The mantle cavity 
is formed by the appearance of a space between the posterior mar- 
1 « Alles Gewordene, im Reiche der Natur, wie in der Geschichte ist nur durch sein 
Werden zu begreifen, und die Entwickelungsgeschichte ist in diesem Sinn fiir den 
Naturforscher vollkommen dasselbe, was die Weltgeschichte fiir die Menschheit 
(Wirbeltheorie des Schadels). BRS 
? De ontwikkelin chiedenis van de cester ( Ostrea edulis), door Dr. R. 
and Embryogénie de VHultre (Ostrea edulis, L.), parle Dr. Horst, Tijdschr. der Ned. 
Dierk. Vereen. Suppl., 1884, pp. 1—63, 1 pl., Leiden. 
3 In this, his observations are not in agreement with Brooks’ observations on 0. 
virginica, in which that author finds the invagination which leads to the develop- 
ment of the shell to coincide with the blastopore. 
