466 F, G. HEATHCOTE. 
development to give rise to fresh cells, which join the meso- 
blast. This is exactly what happens in Julus. 
Metschnikoff has described the formation of the bands of 
mesoblast and their division into somites, but his figures are 
difficult to understand, as he has not drawn either the cell 
outlines or the nuclei. 
The formation of the ventral flexure has been described by 
Metschnikoff, and, as I have already mentioned, was first seen 
by Newport. The flexure is, as I have before said, formed 
between the sixth and seventh post-cephalic segments; that is» 
it marks off from the rest of the body the long eighth segment 
in which the tissues are very imperfectly differentiated, and 
from which the anal segment has yet to be cut off. It is 
from this imperfectly_ differentiated segment that the future 
additional body segments are formed in the later stages of 
development. 
The mesenteron of the adult animal is, as was pointed out 
to me by the late Professor Balfour, marked with a series of 
constrictions corresponding with the external segmentation of 
the body, but no trace of such constrictions has as yet 
appeared. . 
The wide separation of the nerve-cords in the embryo has, 
so far as I know, not been pointed out by any author. 
I propose to reserve for a future paper a more full descrip- 
tion of the development of the nervous system, the circulatory 
system, and the segmentation of the embryo, as well as the 
account of the appendages and other points connected with the 
further development of the embryo. 
The above investigations were entirely carried on in the 
Cambridge Morphological Laboratory. 
Parers REFERRED TO. 
1. BaLprant.—‘ Génération des Vertébres,” p. 258. 
2. Batrour.— Comparative Embryology,’ 1881. 
3. v. BENEDEN.—‘ Fécondation de l’eeuf,’ Liége, 1883. 
4. v. Carnus.— Entwicklung der Spinneneies,” ‘ Zeitschr. fiir wiss. Zool.,’ 
vol. il. 
