set of nerves to muscles, and of another to the skin? Clearly the latter; for there is nothing in the nature of the nerve tissue itself to prevent its serving both functions, as we see in the animal which has only one nerve for both: this nerve is not, as in vertebrata, split up into two, having two different origins, and two different peripheral terminations, but is one nerve, with one origin, sending off branches, here to muscles, and there to surfaces.
In his memoir on the Haliotis, M. Lacaze-Duthiers notices that the optic nerve has two kinds of branches, "les uns, que l'on pourrait nommer tégumentaires, et les autres oculaires proprement dits. Les premiers se distribuent aux téguments et aux tissus contractiles de nature musculaire qui forment les parois du tubercle; évidement ils apportent et la sensibilité et la motilité à ce support de l'organe de la vision." He notices as remarkable, that from the very trunk of a nerve of special sense, branches are given off, which are nerves of general sensibility and nerves of motion. But he contents himself with the supposition that there may be sensitive and motor fibres in this trunk, separate at their origin, though combined together in the trunk. This is, however, irreconcileable with microscopic observation of the molluscan nervous system; for when there are fibres, they are nothing but linear arrangements of the granular mass filling the neurilemma, which enter the ganglion together, and not from separate parts corresponding to anterior and posterior horns.
I will not extend this paper further, by any attempt to assign more definitely the functions of the nerves. The question at issue is: Are we justified in denying a sensory function to the anterior nerves, and a motor function to the posterior nerves? Is the difference between them one of property, or of function?
Having been for some time engaged in the study of a series of typical representatives of several of the chief natural divisions of the Foraminifera,[1] and finding that the general results of my inquiries are fully borne out by the study of other types prosecuted on the like method by Messrs. Rupert Jones and W. K. Parker, I think it desirable to draw the attention of naturalists to them, not merely as fixing the principles
- ↑ See my Researches on Foraminifera, first and second Series, in the Philosophical Transactions for 1856; third Series, op. cit., 1859; fourth Series, op. cit., 1860.
