ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
5U5 
its free edges directed backwards ; these edges grow towards one another, 
but not so fast that they meet by the time the embryo escapes, so that 
at that time the dorsal and ventral walls of the mid-gut still consist of 
scattered cells. At this period the hinder endodermal sack undergoes di- 
vision in the longitudinal direction, and so gives rise to the first liver-sac. 
Galatheidse.* — MM. A. Milne-Edwards and E. L. Bouvier discuss 
in detail the characters of the Galatheidee, the ancestry and relations 
inter se of which are shown by the following diagram. 
Astacidss 
The group is one, the members of which are, like the Paguridae, 
essentially plastic, and adaptational influences have acted on them with 
* Ann. Sci. Nat., lix. (1894) pp. 191-327 (36 figs.). 
