ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
593 
dermal elements ; the spaces are filled by a liquid or by unchanged 
cells, and become the vascular sinuses of the appendage. There is 
nothing in this mode of development which is comparable to the 
portioning-off of the coelom as seen in Annelids and Vertebrates ; there 
is only the formation of clefts which become blood-lacunae. 
A similar mode of development is seen in the mesoderm of the body ; 
its elements, while destroying the nutrient yolk, give rise to the forma- 
tion of spaces which communicate with one another, and become blood- 
lacunae. One of these, that around the intestine, is isolated from its 
fellows, and becomes the circumintestinal cavity. But, before this 
separation is effected, a group of mesodermal cells situated above the 
proctodaeum elongates, and is pierced by a central cavity which unites 
two mesodermal spaces. 
Renal Secretion in Crustacea.* — M. P. Marchal gives a short 
account of the excretory apparatus of Nika edulis , Alpheus ruber , and 
Caridina Desmaresti. He thinks that the production of the urinary 
liquid is not, in Crustacea, due to a simple filtration as the limpidity 
and abundance of the liquid which fills the bladder might lead one to 
suppose ; it is a real secretion with separation of parts of cells. In the 
Paguridse the clear liquid which fills the abdominal bladder contains 
more or less" granular vesicles, often of large size, and sometimes con- 
taining more or less numerous secondary vesicles. When indigo has 
been injected into the animal blue granulations are found in the vesicles. 
It is evident that the bladder takes an important part in secretion. 
The white substance of the Crayfish secretes in the same way as the 
bladder ; its cells are likewise swollen at their extremity into large, clear 
vesicles, distinct from the cell-body. Several vesicles may be found at 
once in one and the same cell of the cortical substance of the Crayfish 
and the labyrinth of other Crustacea ; they give the appearance of a sort 
of palisade, covering the cells. The sacculus also secretes and expels 
parts under the form of vesicles which are often coloured yellow. 
Morphology of Isopod Feet-t — Hr. J. Nusbaum has observed in the 
embryos of Isopoda that all the thoracic feet have the biramose structure 
which is so characteristic of other Crustacea ; it is well known that in 
the adult there is a considerable reduction ; the young type approaches 
most closely that of Nebalia — two-jointed protopodite, five-jointed endo- 
podite, unjointed exopodite, and simple lamelliform epipodite. 
The first foundation of every thoracic foot appears in the form of two 
closely connected papilliform processes of the ectoderm. Simultaneously 
there appears outside each a small disc-like ectodermal thickening. 
The gradual differentiation of the appendages goes on, as usual, from 
before backwards. The inner process of each foundation soon becomes 
longer than the outer, and the foundation of the protopodite is differen- 
tiated somewhat later. The lateral foundation divides into a distal and 
broader part and a proximal and more delicate, which becomes intimately 
connected with the basal joint of the protopodite. It is very probable 
that this not only merely takes part in the formation of the pleura, but 
* Comptes Rendus, cxiii. (1891) pp. 223-5. 
f Biol. Centralbl., xi. (1891) pp. 353-6. 
