''JouS! jan^iry mSs"'] Blastodevm in Grou^ps of Crustacea. 41 
of one kingdom to the other. But, for reasons already assigned, 
this transition, from the vegetable side, is not, and jprohahly cannot 
he, completed under those conditions which prevail below certain 
fixed limits of depth in the ocean. 
If we admit this much as regards the process of shell deposit, the 
ground is at once cleared for us ; and, mutatis mutandis, the elimi- 
nation from the surrounding waters of the elements entering into 
the composition of body-substance, and their conversion into this 
substance by a special vital force inherent in the protoplasmic mass 
itself, and diffused, in all probability, throughout its substance, 
becomes at once as easy of comprehension as any vital act can be,* 
Lastly, if Bathyhius be assumed to constitute the nutritive 
substance of Glohigerina, it follows that, where the largest and 
purest deposits of that Foraminifer present themselves, there must 
be the greatest supply of the nutritive protoplasm. But this is the 
reverse of what we find to be the case, inasmuch as amongst the 
purest Globigerine deposits where these organisms amount to 80 
or 85 per cent, of the entire mass, hardly a trace of gelatinous 
matter is observable. 
VII. — On the Mode of Formation of the Blastoderm in some 
Groups of Crustacea.^ By M. Edouard Van Beneden, Dr. en 
Sciences a Louvain, and M. Emile Bessels, Dr. en Sciences a 
Stuttgart. 
The splendid researches of Kathke on the development of Crustacea 
contain but a few vague statements relating to the formation of 
the blastoderm, and which are not of a character to meet the actual 
exigencies of science. The various naturahsts who subsequent to 
Kathke worked at the development of the Arthropoda have entered 
into this important problem of the mode of formation of the first 
cellular layer of the embryo. The conflicting results at which they 
have arrived are due in part to real differences which occur in the 
manifestation of one and the same phenomenon, and in part to 
differences of interpretation. 
For a long time it had been doubted whether total segmentation 
took place in Crustacea; but the phenomenon has been demon- 
* As no useful purpose would be served, so far as the present question is con- 
cerned, by inquiring at wbat point physical forces enter into competition with 
those which are vital, I have abstained from complicating the subject by reference 
to them. 
t M. Van Beneden, who has very kindly supplied us with the following 
abstract of his memoir to be published in the ' Recueil des Memoires' of the 
Royal Academy of Belgium, has furnished it expressly at oui- request. 
