114 ~=Dr. F. Miller on the Metamorphoses of the Prawns. 
the carapace has, besides the median spine-like process, a shorter 
one on each side, which is directed obliquely forwards and out- 
wards. Moreover, when at the same grade of development, it is 
larger, and was seen as a Zoéa as much as 2°3 mill. in length. 
Younger Zoée, which still want the processes of the carapace, 
are so like those of the former species, that it was not without 
trouble that I learnt to distinguish them by the structure of the 
antenne &c. Upon the median eye of this second species the 
skin usually forms two lentiform thickenings at the sides of the 
bacillus ; once I saw a single larger one opposite to the bacillus. 
Between the two nervous cords of the ventral chain, a minute 
median filament may be distinguished running from ganglion 
to ganglion (this can hardly be wanting in the other species, 
but has not yet been distinctly seen in them). Notwithstanding 
its remarkable similarity to the former species, the course of 
development is somewhat different, the third pair of footjaws 
and the caudal appendages appearing not before, but simulta- 
neously with the thoracic feet. 
A third species was traced from young Zoée 1:2 mill. in 
length, in which the new segments were still of equal length, 
and the first rudiments of the third pair of footjaws and of the 
caudal appendages had just been formed, up to Mysis-like forms, 
3 mill. long, furnished with three imperfect pairs of chele and 
abdominal feet. It is characterized by its bemg abundantly 
armed on the carapace and the segments of the abdomen with 
spinous processes; the median lamina of the caudal fan is also 
produced, in the Mysis-form, into two long pomts. The course 
of development appears to be precisely like that of the first spe- 
cies; the form of the basal joint of the inner antenna in the 
oldest observed larvee (fig. 10) indicates that here also an ear is 
formed similar to that of the first species. 
Of two other species whose Zoée closely approach the three 
preceding in the structure of the antenne, of the spinose upper 
lip, of the multiarticulate second maxilla, of the tail, heart, &c., 
one was only traced to the non-cheligerous Mysis-form ; the other, 
however, which acquires three pairs of chelz, departs so widely 
from the rest in its mode of development, that I postpone the 
history of its metamorphosis for the present, in order to describe 
it separately. 
EXPLANATION OF PLATE IV. 
The figures of the animals are magnified 45 diameters; fig. 2, 180 dia- 
meters; and the rest, 90 diameters. he Roman numbers 1.—XIX. indicate 
the appendages corresponding with the nineteen pairs of the mature ani- 
mal: g, flagellum of the second pair; a, outer, i, inner branch of the 
appendages; L, upper lip; /, heart; J, liver; J’, anterior, 2’, median, 
