in connexion with this, a doubly strict selection will take place.

So much for the development of the higher Crustacea.

A closer examination of the developmental history of the lower Crustacea
is unnecessary after what has been said in general upon the historical
significance of the young states, and the application of this which has
just been made to the Malacostraca. We may see, without further
discussion, how the representation given by Claus of the development of
the Copepoda may pass almost word for word as the primitive history of
those animals; we may find in the Nauplius-skin of the larvae of
Achtheres and in the egg-like larva of Cryptophialus, precisely similar
traces of a transition towards direct development, as were presented by
the Nauplius-envelope of the embryos of Mysis and the maggot-like larva
of Ligia, etc.

It will be sufficient to indicate an essential difference in the process
of development in the higher and lower Crustacea. In the latter all new
body-segments and limbs which insert themselves between the two terminal
regions of the Nauplius, are formed in uninterrupted sequence from
before backwards; in the former there is further a new formation in the
middle of the body (the middle-body), which pushes itself in between the
fore-body and the abdomen in the same way, as these have done on their
part between the head and tail of the Nauplius. Thus, that which appears
probable even from the comparison of the limbs of the adult animal,
finds fresh support in the developmental history, namely, that the lower
Crustacea, like the Insects, are entirely destitute of the region of the
body corresponding to the middle-body of the Malacostraca. It seems
probable that the swimming feet of the Copepoda, as also of the pupae of
Cirripedia and Rhizocephala, represent the abdominal feet of the