ROSACETTS, LIXCK (COMATULA ROSACEA OF LAMARCK). 
517 
to a much later period in the pedunculated condition than that of A. rosaceus; the dis- 
engagement of the latter species from its stem constantly occurs between the middle of 
August and the middle of September. The capture of the specimen described by Sars 
in March would seem to indicate that the development of the Pentacrinoid of A. Sarsii 
extends over nearly a year. 
The early portion of the history of the development of Antedon described in the fol- 
lowing pages divides itself naturally into two stages. 
The Echinoderms present in the most marked degree a peculiarity which seems to be 
only imperfectly indicated in the other invertebrate subkingdoms. This peculiarity 
consists in the successive development from a single egg, of two organisms, each appa- 
rently presenting all the essential characters of a perfect animal. These two beings 
seem to ditfer from one another entirely in plan of structure. The first, derived directly 
from the germ-mass, would appear at first sight to homologate with some of the lower 
forms of the Annulosa ; the second, subsequently produced within or in close organic 
connexion with the first, is the true Echinoderm. The extreme form of this singular 
cycle, in which the development of a provisional zooid as a separate, independent, living 
organism, is carried to its full extent, is by no means constant throughout the whole 
subkingdom, although its existence has been established for all the recent orders. In 
each order it appears to be exceptional, and in certain cases it is known to be carried 
to its most abnormal degree in one species, while in a closely allied species of the 
same genus the mode of reproduction differs but slightly from the ordinary inver- 
tebrate type. 
To avoid ambiguity in the discussion of such singular relations, I believe it is necessary 
to introduce certain new terms. For an organism which possesses all the apparent cha- 
racters of a distinct animal, which is developed from the germ-mass, and which maintains 
a separate existence before the appearance of the embryo, I would propose the term 
pseudembryo ; and for all the appendages which homologate with the whole or with 
parts of such a pseudembryo, even although they do not assume fully the characters of 
a distinct animal form, I would propose the term pseudembryonic appendages. The 
same prefix may distinguish the organs of the temporary zooid, where such exist, 
pseudostome, pseudocele , pseudoproct, &c. The reason for the retention of this series 
of terms, and for the rejection as applied to the provisional organism of the ordinary 
terms “ embryo ” and “ larva,” will be fully discussed hereafter. 
The first stage includes the development, structure, and life-history of the pseud- 
embryo. 
While the special external form of the pseudembryo is still perfectly retained, and 
while its special functions are still in full activity, the form of the pentacrinoid embryo 
is gradually mapped out within the provisional zooid, and the permanent organs of the 
embryo are differentiated within its sarcode-substance. The pseudembryo then becomes 
gradually distorted by the embryo developing within it, its special assimilative and loco- 
motive organs disappear, and the external layer of its sarcode-substance subsides into the 
