ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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rogions ; of those the anterior is devoted to the absorption of tho products 
of digestion ; in tho middle region digestion occurs, and in the hindor 
region the faeces are found. 
The fact that digestion occurs in a region of the gut posterior to that 
which is occupied in the absorption of tho products, is probably without 
a parallel in the Animal Kingdom, except perhaps among the simplest 
Coelentera. 
The authors give an account of the processes of digestion as studied 
in specimens fed by pouring beaten yolk of egg, milk, carmine, &c., ovor 
the bottom of the dish in which they are living. Owing to the trans- 
parent nature of the living Daphnia , observation is quite easy. For the 
details of these observations reference must be made to the original, but 
it is of importance to note that there is here a profound difference 
from the higher Crustacea, in so far as the stomodaeal and procto- 
daeal portions only take part in the deglutition and defaecation of 
food ; the injecta and ejecta are not lodged in them, but merely hurried 
through. 
The cells of the mesenteron have a hyaline border, which is best 
developed in the region in which the absorption of fat was found to take 
place ; this corresponds with observations made on other animals. 
Histological characters of the cell-substance of the cells lining the 
mesenteron afford further evidence of a differentiation of the epithelium 
into regions corresponding to those which actual observation of the pro- 
cesses of digestion shows to exist. The cells of the middle region of the 
mesenteron are specially characterized by the presence under certain 
conditions of granules which appear to be secretory ; so that the cells 
which bear them are gland-cells, engaged in the elaboration of a diges- 
tive ferment or ferments. At the posterior end of the mesenteron the 
gland-cells secrete remarkably compact groups of granules which 
appear to glue together the scattered faecal particles into a compact 
mass. 
The stomodaeum consists of a muscular tube lined by a simple low 
epithelium, which is covered internally by a cuticle; the proctodaeum 
has much the same structure, but its basement membrane is especially 
well developed. The basement membrane of the gut is the actively 
contractile organ which brings about peristalsis. It is continuous over 
the whole mesenteron, and is thin, but very high and very elastic ; it has 
imbedded in it protoplasmic strands which are presumably the contractile 
elements. These are flattened and are arranged in a longitudinal and a 
circular series. No traces of nuclei have yet been detected in the base- 
ment membrane. 
Ascothoracida.* — M. Racovitza has an analysis of a memoir by 
M. N. Knipowitsch on the Ascothoracida ; of this group he has studied 
the Laura Gerardise of Lacaze-Duthiers and Dendrogaster astericola , a 
new genus from the White Sea, which inhabits the coelom of Echinaster 
sanguinolentus and of Solaster endeca. In addition to these forms which, 
like Petrarca bathyactidis , are endoparasitic, there is Sinagoga mira , 
which is ectoparasitic. The author regards the group as a suborder of 
the Cirripedia, the other suborder being composed of the thoracic, 
* Arch. Zool. Exper., i. (1893) pp. xvii.-xix. 
