[ 858 J 
XXVI. On Tomopteris onisciformis, Eschscholtz. By Wirra B. CARPENTER, Esq., | 
| M.D., F.R.S., FLS., F. G.S. | 
Read Jan. 20th, 1859. 
THE animal which forms the subjeet of the present communication is one which has 
not very frequently presented itself to the notice of zoological inquirers; and it is not a 
little singular that almost every one under whose observation it has fallen has given 
an account of its structure differing in some essential particulars from that of other 
observers.. This circumstance may of course be readily accounted for on the hypothesis - 
_ that the several specimens examined have belonged not to the same, but to different - 
specific types. I cannot but believe, however, that a careful comparison of the pub- 
lished accounts will lead others, as it has led myself, to the conclusion that all the speci- 
mens described are referable to one and the same type, and that the differences are 
chiefly those of phase or stage of development. For it is remarkable that the accordance 
should be closest in those details of structure which might be expected, on the hypothesis 
of specific difference, to be most liable to vary; whilst the diversities are greatest in those 
features which seem most liable to undergo modification in the progress of development. 
I shall first give a detailed account of my own observations, and shall then compare 
them with the descriptions which I have since found to have been given of this creature 
by those to whom it had already. presented itself. My observations were made in the. 
month of September last, on specimens captured in Lamlash Bay, Arran. I was for- 
tunate in being able at the time to obtain the assistance of Mr. George West, whose 
intelligence and scrupulous accuracy as a microscopic draughtsman are well known to all 
Who have employed him; and the drawings which accompany this communication having 
. been all executed by him with the objects immediately before him, and under my own - 
direction as to the points to which his attention should be specially given, I cannot but 
consider that they have a value much greater than can be attached to many of the — 
_ Sentations heretofore published, most of which seem to me to be little better than ideal 
| diagrams. ; | j z . . e 
The study of this animal, I may say i» limine, presents peculiar difficulties, from its 
incessant restlessness, and from the circumstance that its delicacy is such, that confinement 
is Speedily fatal to it, its tissues and organs exhibiting a manifest tendency to disintegra- 
tion some time before it ceases to move. We had, however, the great advantage of being 
able to make our obsérvations on several specimens in the younger and simpler stage which 
I shall first describe ; and I feel sure that we had accurately mastered all the most important 
features of its structure, before I met with the remarkable, and not a little perplexing form, 
Which I think I cannot be wrong in regarding as a more advanced stage of the same. 
VOL. XXII. : 9A 
