GLAND.
granules (the so much talked of (who) of the liver and other conglomerate glands.
Such, then, arc the more simple forms of the glandular organs; and if we proceed to those are more complex, nu difficulty is expe rienced in proving, by the aid of comparative and developmental anatumy, that the structure, although it becomes more and more developed, is in character essentially the same. The inquiries of the anatomist in this respect are greatly facilitated by the existence of an univer sal law connected with the process of organiza tion, in accordance with which it happens that, whenever any particular gland first appears in the animal series, it presents invariably the simplest form of the glandular structure, al though this same gland may subsequently attain in the higher classes the most intricate formation. It is for this reason the salivary glands are so simple when they first appear in birds, the pancreas in fishes, and the liver in insects.
Ample confirmation of this gradual transition from simple to compound, which is in fact only another instance of the great laws which regulate the formation of the whole animal creation, is afforded by following any of the more intricate glands through the several stages of their development. Thus, if the pancreas be examined in its rudimentary state, it will be perceived that, like the mucous follicle, it is composed either of a fluid sac or of a tube more or less complicated. In the class Cephulopoda, the individuals of which are so remarkable by the complexity of their internal organization, the pancreas consists either of a simple sac opening into the intestine near the gizzard, (see fig. 219, p, fig. 220,f, vol. i. p. 533), or of a spiral canal, (fig. 221, j; p. 535,) the secerning surface being increased by a number of laminal. In most fishes there are numerous fluid appen dages placed near the pyloric extremity of the stomach, ( appendices pylorica.,) which are with
propriety regarded as constituting a rudimen tary pancreas, (fig. 212,) and which, in the in Fig. 212.
4133 Fig. 213.
stance of the Sturgeon and Swordfish are ag gregated into a glandular mass.' (See fig. 46, v01. i, p. 115.) The liver is certainly the most intricate struc ture of all the glandular organs when examined in the higher animals ; and yet, if we descend to the lower classes, which present, as it were, a natural analysis of the various parts of the animal machine, the texture becomes suffici ently simple. One of the most simple forms of this organ is probably furnished in the lain (micas terrestris; at least I have seen in that animal, in a few instances, a beautiful appear ance of email tubuli composing the yellowish substance which coats the Intestine, and which is thought by some authorities to constitute the liver. In many insects, Crustacea and other Articulata, the biliferous organs consist of fluid sacs proceeding from the stomach or intestine, and often assuming the appearance of tubes, but always closed at their distal extremities. In some instances these tubuli are very simple, (see fig. 37, d, vol. i. p. 111,) but in other cases they are more complicated, and present a ramified arrangement; and in this manner the structure evidently approaches that of the most compound or conglomerate glands. The liver of the Lobster presents an excellent illustration of the meal tubuli which constitute the secre ting structure of so many species of glands.
By cutting out a por Fig. 214. tion of this organ, and slightly unravelling the tubes by moving the section in water, the canals ending in cul de-sac are beautifully seen, and if slightly magnified, it is found that they closely re semble the pyloric ap pcndages of fishes. The • Haller remarks that. in the Skate and Shark, the pancreas is similar to that of higher animal.
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