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IX. On the Ernbryogeny of Antedon rosaceus, LincJc (Comatula rosacea of Lamarck). 
By Professor Wyville Thomson, LL.D., F.B.S.E., M.B.I.A., F.G.S., &c. Com- 
municated by Thomas Henry Huxley, F.B.S. 
Received December 29, 1862, — Read February 5, 1863*. 
In the year 1827 Mr. J. V. Thomson, Deputy Inspector-General of Military Hospitals, 
described and figured what he believed to be a new recent Crinoid, under the name of 
Pentacrinus Europceus ; and in June 1835 communicated to this Society a “Memoir on 
the Star-fish of the genus Comatula , demonstrative of the Pentacrinus Europceus being 
the young of our indigenous species.” In this memoir the author describes and figures 
a series of Pentacrinus Europeans from its earliest stage, in which it is represented as 
“ an attached ovum in the form of a flattened oval disk, by which it is permanently fixed 
to the point selected, giving exit to an obscurely jointed stem ending in a club-shaped 
head”; to its most perfect attached condition, in which the head is compared with, and 
found closely to resemble the youngest free Antedon taken with the dredge. 
The period of the disappearance of the pentacrinoid larvae on the oar-weed exactly 
corresponds with that of the appearance of the most minute free Antedons in the water. 
Mr. Thomson’s observations were conclusive. I am not aware that they have hitherto 
been repeated in detail on the European species, but the “ pentacrinoid ” stage of Ante- 
don has ever since been the frequent and familiar prize of the dredger, the wonderful 
beauty and gracefulness of its form and movements, and its singular relations to the 
Echinoderm inhabitants of modern and of primaeval seas, rendering it an object of ever 
recurring admiration and interest. 
The remarkable discoveries of Professors Sars and Johannes Muller on the meta- 
morphoses of the embryo and its appendages in other Echinoderm orders rendered it 
probable that the germ of Antedon might pass through some earlier transitional stage 
before assuming the fixed pentacrinoid form. 
Dr. W. Busch undertook this investigation, and for this purpose he visited Orkney in 
J uly 1849, and procured a supply of specimens in Kirkwall Bay. As those of Dr. Busch 
are the only recorded observations on the early stages in the embryology of the Crinoids, 
I shall briefly abstract his results published in Muller’s ‘ Archiv,’ 1849, and more fully 
* Subsequently to tbe reading of this paper it was arranged that the author should take up a somewhat later 
stage in the development, which he had at first intended to leave to Dr. Carpenter. The paper was accordingly 
returned to him that it might receive the necessary additions ; but no alteration of importance has been made 
in the description of the earlier developmental stages, which formed the subject of the memoir presented to the 
Royal Society. 
4 A 
MDCCCLXV. 
