414 Miscellaneous. 
possesses at its two ends a certain quantity of nutritive globules 
floating in the liquid which occupies the whole cavity. The endo- 
dermic cells, which at first were as distinct as those of the ecto- 
derm, have been more slowly evolved, neither increasing in number 
nor becoming differentiated so much as those of the external lamella. 
They are charged with fatty globules, have acquired a clavate form, 
and their contours have become a little confused. The larva ad- 
heres by its larger end, which was carried in front during its errant 
life, which is usually very short. The smaller end becomes gradu- 
ally depressed, forms at first an ectodermic plate, in the middle of 
which there often rises a knob representing the extremity of the 
larva, then becomes invaginated and constitutes the cesophageal sac, 
the bottom of which has to become perforated to place the mesen- 
teric cavity in communication with the exterior. 
As these phenomena take place the ectoderm becomes thickened 
by the appearance of a conjunctive layer, which will become the 
pseudomesoderm. A primitively structureless substance is secreted 
by the cells, and interposes itself between these ectodermic elements, 
which become less close-pressed by this means alone. Below, this 
conjunctive substance accumulates and receives into its mass cells 
which become detached from the peripheral layer. In Sympodium 
these migratory cells of the ectoderm early give origin in their 
interior to small calcareous nuclei, which become the sclerites. These 
corpuscles enlarge rapidly as the conjunctive layer thickens, while 
the cellular ectoderm diminishes in importance and now covers the 
pseudomesodermic zone only with one layer of flat cells. 
In the Clavularie, and especially in Clavularia petricola, the 
ectoderm at the beginning undergoes quite different differentiations. 
The appearance of the sclerites is late. On the other hand, the 
errant larva already possesses a complex ectoderm. Cells with 
urticating threads have become differentiated in the outer portion ; 
in the deeper region the cells are prolonged into the midst of the 
conjunctive substance secreted by filaments which resemble the 
epithelio-muscular and epithelio-nervous histological elements of the 
Actiniaria. The mesenteric dissepiments are always formed before 
the cesophageal invagination, in proportion as the larva becomes 
fixed. In Sympodium they present a great regularity from the 
very first. In Clavularia petricola we see as many as twenty-six 
primitive dissepiments appear at the bottom of the mesenteric cavity, 
their axis being formed by conjunctive streaks attached to the base 
of the ectoderm. It is only at the moment when the mouth is 
formed that these dissepiments become regular; eight of them 
grow rapidly to join the cesophagus, while the others become effaced 
by degrees. 
Side by side with the normal embryonic process, Sympodium 
has presented us with facts of the highest interest, showing, in the 
larvee of these Coelenterata, a remarkable plasticity in the course of 
their morphological and histological differentiation. 
We shall here mention only the most important peculiarities. 
Tn the same laying of Sympodium we find, together with normal 
