e. Of the distribution of the striped and tinstriped fibres in the animal kingdom.— The striped fibres have been found in all ver tebrated animals, and in Insects, Crustacea, Cirropods, and Arachnida. Future researches will probably discover them even more exten sively diffused. But in the lower animals, especially when they are of small size, we find, as formerly mentioned, that the distinctive cha racters of the two varieties begin to merge into one another and be lost. The transverse stripes grow irregular, not parallel, interrupted ; a fibre at one part will possess them, at another part will be without them; and even the peculi arities of the unstriped fibres are sometimes no longer to be met with in parts which are un doubtedly muscular, as the alimentary canal of small insects. It is evident that here the elementary fibres, if of their usual bulk, would be greatly disproportioned to the requirements of the case, and consequently even the minute ultimate fibre seems to be reduced within limits which remove from it those anatomical characters by which alone we can positively aver its existence. Considering, however, the circumstances which have been already ad verted to in this article, as determining the size of the elementary fibre in all animals, we should not be justified in denying the same muscular tissue to exist here which in the higher and larger forms of life assumes the figure and hulk of the elementary fibre ; and by the same mode of reasoning it may be concluded, that a tissue having the same properties as the striped fibre, and indeed essentially identical with that of which they consist, may possibly be the effective agent to which are due those wonderfully vivacious movements witnessed in the bodies of many of the minutest infusoria, where the best microscope can hardly do more than discern the organs thus put in motion.
And it seems far from an unphilosophical view of the nature of ciliary motion, to refer it to the contractions of a tissue not entirely dif ferent in kind from the muscular. The ele mentary fibres of muscle, diminutive though they he, and hardly discernible with the eye, are yet gross organs in comparison with those which the microscope enables us to conceive capable of being formed out of them, without any necessary destruction or even injury of their contractile power.
f. Chemical constitution.—There is little to add on this subject to what will be found under the head of Fisaiisr. By the aid of the mi croscope, however, our knowledge has been rendered somewhat more precise, as to the chemical properties of the elementary struc tures existing in the fibres. If any substance capable of dissolving fibrine (as liq.ammonim) be added to the muscular fibre, this is seen to swell, to lose more or less completely its trans verse and longitudinal markings, and to exhibit at once those corpuscles or cytoblasts, which before lay concealed among the sarcous ele ments. These corpuscles and the sarcolemma are not affected, but the sarcous elements are almost entirely taken up. But for however long a time the fibre be exposed to the alka line menstruum, there will always remain a kind of web, of extreme tenuity and trans parency, from which the sarcous elements ap pear to have been withdrawn. This may be seen in a transverse section of a muscle that has been thus treated, then washed and dried. I have not been able to detect in it any sort of structure.* ( W. Bowman.)