190 REPORT—1850. 
sideration of the historical part of the subject. The genus is a very important one, 
especially as regards the relation of the South African Fauna with that of Australia 
and New Zealand, and may be thus defined :— 
Polypidom growing from the base with a more or less distinct stem, consisting 
of a congeries of horny tubes. ‘The branches dichotomous, composed of calcareous 
cells arranged in linear series, and arising, one from the upper and back part of 
another, a flewible joint intervening between them. At the dichotomous divisions of 
the branches, which take place after a variable number of cells, the duplication of 
the series is effected by one of the cells giving off laterally a second sessile cell, from 
the upper and back part of which, as in the parent cell, the subsequent cell and series 
arise. It is in respect of the mode of division of the branches, that the species above 
referred to differs from the others, and would appear to constitute a distinct generic 
form. 
The openings of the cells are all on one face of the branch, and vary in different 
species iu shape, &c., as does the sculpture on the cells, their form and size, &c. 
The cells are always furnished with lateral appendages or als, which in most species 
support longer or shorter spines, which apparently are readily detached; but in some 
cases the lateral appendages assume the form of cup-like cavities or are Avicularia. 
This genus appears to be in great measure confined to the southern hemisphere, and 
there is probably no species of it in the European Fauna. A species is described 
and figured in the great French work on Egypt (Catenicella Savignyi), but this may 
probably have been obtained from the Red Sea. It approaches very nearly to one of 
the South African species. There is also in the Mediterranean a Polyzoon, named by 
Audouin Eucratea Lafontii, and also figured in the work just cited, which however 
differs from Eucratea in having flexible joints and in other respects, and which would 
seem to be allied with that among the South African forms, which differs in its 
mode of division from the other true Catenicelle. 
The principal seat of this genus would appear to be in the Australian seas, for in 
the rich collection of zoophytes sent home from H.M.S. Rattlesnake, not less than 
sixteen distinct species of this genus occur, all differing however from the South 
African. And from New Zealand another species has been named by Mr. Gray 
Catenicella bicuspis, which is probably distinct from any of ce Australian forms, 
though closely resembling one of them. 
Examples of Exuviation, or the Change of the Integuments of Animals in the 
Crustacean Tribes. By Sir Joun Granam Datryett, Bart. 
All animals are invested by a skin, an external covering or integument of various 
quality. In general the skin simply expands with the growth of the subject which 
it invests, but where the integument is not susceptible of such enlargement, nature 
has provided effectual substitutes in its place. This is most favourably illustrated 
by the history of the crustacean tribes. 
While occupied with the Cancer Menas, the Shore or Harbour Crab, a dingy 
brown specimen, A, of medium size, with one limb white, was put outside the window 
on a summer evening, in a capacious glass vessel of sea-water. In the morning, a 
form exactly resembling its own, only somewhat larger, lay in the vessel. This was 
a new shell, exuviation having taken place in the night. The resemblance was 
complete ; every organ, even the white limb, was seen in both. The natural colour of 
this species is green, or it is often variegated green and white, and is sometimes reddish. 
Another specimen, B, was caught of smaller size, the opposite extremities of the 
limbs being only 13 lines asunder, its colour green, with three white patches on the 
back. In the course of little more than a year five exuviations took place at irregular 
intervals, the new shell and animal being successively larger on each. The third 
shell came in uniformly green, the white being entirely obliterated. The limbs ex- 
panded two inches and a half on the fourth exuviation. 
As this subject was a male, a female of about the same size was introduced into 
its vessel soon after the fifth exuviation, but only after they were gorged with food, 
to avert hostilities. Both gave unequivocal symptoms of satisfaction. Their union 
followed, the breast-plate or (more properly) the apron of each being folded back. 
This female underwent several exuviations, Its shell was originally of a beau- 
