ma MUSCIDJu 



structure of the parts of the suckers, it was immediately perceived 

 that the function ascribed to them by Dr. Derham and Sir E. Home 

 is quite incompatible with their organisation. " Minute hairs, very 

 clossly set and directed downwards, so completely cover the inferior 

 surface of the expanded membranes, improperly denominated suckers, 

 with which the terminal joint of the foot of flies is provided, that it 

 cannot possibly be brought into contact with the object on which 

 those insects move by any muscular force they are capable of exerting. 

 The production of a vacuum between each membrane and the plane 

 of position is therefore clearly impracticable, unless the numerous 

 hairs on the under side of these organs individually perform the 

 office of suckers ; sad there does not appear to be anything in their 

 mechanism which in the slightest degree countenances such an 

 hypothesis. When highlv magnified, their extremities, it is true, are 

 sen to be somewhat enlarged ; but when they are viewed in action 

 or in repose, they never assume a figure at all adapted to the forma- 

 tion of a vacuum." Moreover, on enclosing a House-Fly in the 

 receiver of an air-pump, it was demonstrated to the entire satisfaction 

 of several intelligent gentlemen present that the fly, while it retains 

 its vital powers unimpaired, can not only traverse the upright sides, 

 but even the interior of the dome of on exhausted receiver ; and that 

 the cause of its relaxing its hold, and ultimately falling from the 

 station it occupied, was a diminution of muscular force, attributable 

 to impeded respiration. Hence Mr. Blackwall U induced to believe 

 that insects an enabled to take hold of any roughness or irregularity 

 of surface, by means of the fine hairs composing the brushes, the 

 most carefully polished gloss not being found free from flaws and 

 imperfections when viewed in a favourable light with a powerful lens. 

 A still different opinion has been maintained by other authors upon 

 this subject, who, setting aside all idea of a vacuum, have conjectured 

 that the suckers, as they have been termed, contain a glutinous secre- 

 tion, capable of adhering to well-cleaned glass ; thus Abln5 de la 

 Flucho states that when the fly marches over any polished body, on 

 which neither her claws nor her points can fasten, she sometimes 

 compresses her sponge, and causes it to evacuate a fluid, which fixes 

 her in such a manner as prevents her falling, without diminishing the 

 facility of her progress. " But it is much more probable," he adds, 

 " that the sponges correspond with the fleshy balls which accompany 

 the claws of dogs and cats, and that they enable the fly to proceed 

 with a softer pace, and contribute to the preservation of its claws, 

 whose pointed extremities would soon be impaired without this pre- 

 vention." Notwithstanding the ridicule which has been thrown upon 

 this opinion in a recent entomological work, it appears, from still 

 more recent investigations, to be the best founded of any hitherto 

 advanced. Thus, in general, the foot of the fly is described as being 

 composed of two hooks and two flaps, or hollow cups, which act as 

 suckers. Rymer Jones, in his ' General Outlines of the Animal 

 Kingdom,' 1841, says "The House-Fly is furnished with a pair of 

 membranous flaps, which, under a good microscope, are seen to be 

 covered with innumerable hairs of the utmost delicacy ; these flaps, 

 or suckers, as they might be termed, adhere," Ac. 



The structure of the foot of the fly has recently been examined by 

 Mr. Hepworth, who says : " The flap varies in form in different 

 species, from an irregular circle to that of on irregular triangle ; and 

 viewing it from one side, it is somewhat thicker at the base (near 

 its attachment), the under surface being, when isolated, convex, but 

 perfectly flat as a whole, when applied to a surface of that form. It 

 appeared to be composed of on upper and under layer of oreolar 

 tissue, or something similar to it, between which a bundle of tubes, 

 along with the fasciculi of a large muscle pass ; these are placed at its 

 base, and (sometimes protected by a ' coat of mail,' formed by long 

 scales overwrapping each other as a Venetian blind, or in alternate 

 ones, as the scales of a fish, Ac., but more frequently wanting) expand 

 in a radiated form ; each tube, as it passes along with its fellows on 

 each side, gives off a number of tubules alternately with them ; these dip 

 downwards from the under surface, and become expanded into trumpet- 

 shaped extremities, the flap becoming thinner and thinner as it 

 approaches its margin, which sometimes terminates in an irregularly 

 serrated edge, and at others by finely pointed hairs. The fly has the 

 power of attaching itself to smooth surfaces by these trumpet-shaped 

 extremities, and also of secreting a fluid from them, when vigorous, 

 and it has occasion to make extra exertions ; but in a partially dormant 

 state (the best for making observations), it does not appear to be able 

 to give out this secretion, although it can still attach itself; indeed 

 this fluid is not essential for that purpose : when it is secreted, it is 

 deposited on the glass with great regularity. I have often attempted 

 to preserve these markings by applying colouring matter whilst they 

 were moist, but have not yet succeeded. The tubules are often seen 

 protruding from under the margin of the flap in a semi-arch-like form, 

 giving it a fringed appearance. The foot of the male Dytuciu is a 

 type, not only of many of the beetle tribe (not aquatic), but of the 

 whole of that of flies possessed of flaps. The first joints of the tarsus 

 of the anterior legs of this bisect are extremely dilated, so as to form 

 a broad circular palette. On examining the inferior surface of this 

 expanded portion, it is seen to be covered with a great number of 

 sucking caps, two or three being larger than the rest, but they form 

 collectively a wonderful instrument of adhesion." (' Quarterly Journal 

 of Microscopical Science.') 



MUSCLE. v-< 



MUSCLE is an animal tissue composed of bundles of soft and 

 usually reddish fibres, endowed with a peculiar power of contracting. 



The muscles are divided into two classes the voluntary and the 

 involuntary. The former class, those over which the will exercises a 

 direct control, are subservient to all the actions by which the animal 

 is placed in active relation with the external world, as in all the 

 motions of the limbs, of speech, of the eyes, ears, Ac., and they are 

 therefore often called the muscles of animal life ; the latter class, 

 comprehending those whose actions are connected with the internal 

 and nutritive functions of the body, over which the will has no imme- 

 diate or constant control, form the muscular system of organic life, as 

 the heart, the muscular coat of the stomach, Ac. 



Each voluntary muscle is composed of a number of parallel or nearly 

 parallel fleshy bundles, inclosed in coverings of cellular tissue, by 

 which each is connected with and at the same time isolated from 

 those adjacent to it Each bundle is again divided into smaller fas- 

 ciculi similarly ensheathed, and so on through an uncertain number 

 of gradations till we arrive at the muscular fibre, the only definite and 

 fixed form in the system, and the only part which possesses characters 

 common to the muscles of all classes of animals. The muscles being 

 thus divided, each fibre or each fasciculus may be regarded as a sepa- 

 rate contractile organ, which though usually acting in concert with 

 those adjacent to it, is capable of independent contraction ; and the 

 power of a whole muscle will thus be equal to the sum of the powers 

 of its separate fibres, and will bear a direct proportion to their 

 number. 



The two forms of muscular fibre differ extremely in their micro- 

 scopic characters. The fibres of the voluntary muscles, as well as the 

 fibres of the heart and some of those in the oesophagus, are Striped or 

 Striated ; while all other muscles, including those of the alimentary 

 canal, the uterus, and bladder, all of which are involuntary, ore 

 Unstriped or Non-Striated. 



The elementary fibres of the voluntary muscles are arranged in sets 

 parallel to one another, whilst those of the involuntary muscles 

 usually cross at various angles, and interlace, forming membranous 

 organs, inclosing a cavity which their contraction serves to constrict. 



The Striated Fibres ore usually of about the same length as the 

 muscle to which they belong. In the Sartorius they often exceed two 

 feet in length, while in the Stapedius (in the middle ear) they ore not 

 two lines. They vary in diameter from l-60th to MSOOth of an 

 inch, being largest in Crustacea, Fish, and Reptiles, where their irrita- 

 bility is most enduring, and smallest in Birds, where it is most 

 evanescent In Man their average diameter is 1-4 00th of an inch. 

 The fibre always presents upon and within it longitudinal dark lines, 

 along which it subsequently splits up into fibrillic ; but it is by a 

 fracture alone that these fibrilUe are obtained ; they do not exist as 

 such in the fibre. Sometimes, on the application of violence, cleavage 

 takes place in a different manner, in a plane at right angles to the long 

 axis of the fibre. In this case discs, and not fibrillic, are obtained ; 

 and the cleavage is just as natural as the former, though less frequent 



A ** 1. 



FnfmenU of Elementary Fibre* , Knowing a Cleavage in opposite direction*. 



A, Longitudinal Cleavage : the longitudinal and trannvcnic linen arc both 

 seen ; c, fibrlHu) separated from one another by violence at the broken 

 the nbre, and marked by trannvcrM lino equal In width to those on the fibre ; 

 r', ", represent two appearances commonly presented by the acparato tingle 

 tibrillic (more highly magnified). At ' the borders and transverse lines are all 

 I., ihitly rectilinear, and the Included spaces perfectly rectangular. At c" the 

 borders are scalloped and the spaces bead-like. When moat distinct and definite, 

 the flhrilla presents the former of these appearances. 



II, Transverse Cleavage : the longitudinal lines are scarcely visible ; a, incom- 

 plete fracture following the opposite surfaces of * disc, which stretches across 

 the Interval and retains the two fragments In connexion. The edge and surface 

 of this disc are aeen to be minutely granular, the granules corresponding in size 

 to-the thlckocM of the dlse, and to the distance between the faint longitudinal 

 linen. 6, another disc, nearly detached. V, detached disc more highly mag. 

 nified, showing the sarcoui elements. (Bowman, in ' Todd's Cyclopedia.') 



Hence the fibre must be regarded neither as a bundle of fibrillic 

 nor a pile of discs, but as " a moss in whose structure there is an 

 intimation of the existence of both, and a tendency to cleave in the 

 two directions." The same particles compose the disc and the 

 tibrilla, and they have received the names of the primitive or earcous 



