416 Miscellaneous. 
cavity (partim), but really to the digestive canal. Consequently, 
the lining of the portion enclosed by embolé represents not meso- 
blast, but hypoblast. 
According to this, the development of the digestive canal must be 
understood to proceed as follows :—At the oral pole of the ovum 
there appears a depression, which is clothed by the epiblast which 
is driven inwards. This depression, becoming deeper, pushes back 
the subjacent layer, that is to say the hypoblast, which yields and 
becomes eaten away after a certain time. In this way a communi- 
cation is established between the hypoblastic cavity and the exterior, 
by the medium of a permanent mouth. As a matter of fact the 
archenteron does appear trilobed in front, but the lobes belong to 
the digestive canal. Later on, the lateral lobes commence to de- 
generate and disappear. Then the blastopore closes, and the anus 
is formed in its vicinity. 
At the same time as the atrophy is taking place in the lateral 
lobes of the archenteron, a delamination sets in between the epi- 
blast and hypoblast, and a mesoblastic cavity is formed, which will 
subsequently become the general body-cavity of the animal. 
In proportion as the posterior portion of the embryo increases in 
size, the separation between the two layers increases, and there is 
constituted posteriorly a spacious cavity, traversed by two mesen- 
teric bands, of mesoblastic origin, which attach the digestive canal 
to the somatic walls. These mesenteries are finally absorbed in 
the posterior region of the body, where the somatic cavity is single 
in the adult. 
On the sides of the terminal intestine cellular proliferations arise 
at an early period, whence are derived the male and female organs. 
The latter, therefore, are not developed, as has been asserted, in the 
cavity of the intestine, but outside it, in the space resulting from 
the delamination of the epiblast and hypoblast, of which we have 
spoken above. We found it impossible to determine with certainty 
the part played by each of these two layers in the formation of the 
genital glands, and consequently to discover whether Edouard van 
Beneden’s theory is here confirmed. 
We have nothing to add to what has been stated as to the mode 
of formation of a cephalic and somatic section of the general body- 
cavity. 
We ascertained that the musculature, which is tolerably complex 
in the cephalic region, is derived from the mesoblast of the corre- 
sponding division. 
We were not able to study in sufficient detail the development 
of the nervous system. Nevertheless, from the ensemble of our 
observations upon the embryogeny of Sagitta, we suspect that this 
type is not so distant from the Vertebrates as is generally supposed. 
Sagitta, the Ascidians, and Amphiowus appear to us to constitute 
a special group, in which we observe the appearance of the earliest 
lineaments of the Vertebrates, and which, for this reason, we might 
designate by the title “‘ Prevertebrates.”—Comptes Rendus, t. exiv. 
no. 1 (Jan, 4, 1892), pp. 28, 29. 
