GLAND. 



433 



granules (the so much talked of acini) of the 

 liver and other conglomerate glands. 



Such, then, are the more simple forms of the 

 glandular organs ; and if we proceed to those 

 which are more complex, no difficulty is expe- 

 rienced in proving, by the aid of comparative 

 and developmental anatomy, 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 Cephalopoda, 

 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 

 Jig. 219, p, fg. 220,/, vol. i. p. 533), or of a 

 spiral canal, (fg. 221, /, p. 535,) the secerning 

 surface being increased by a number of laminae. 

 In most fishes there are numerous fluid appen- 

 dages placed near the pyloric extremity of the 

 stomach, (appendices pyloric&,) which are with 

 propriety regarded as constituting a rudimen- 

 tary pancreas, (fg. 212,) and which, in the in- 



Fig. 212, 



Fig. 213. 



Fig. 214. 



stance of the Sturgeon and Swordfish are ag- 

 gregated into a glandular mass.* (Seefg. 46, 

 vol. 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 lum- 

 bricus terrestris ; at least I have seen in that 

 animal, in a few instances, a beautiful appear- 

 ance of coecal 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. Ill,) 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 crecal tubuli which constitute the secre- 

 ting structure, of so many species of glands. 

 By cutting out a por- 



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- 

 pendages of fishes. The 



* Haller remarks that, in the Skate and Shark, 

 the pancreas is similar to that of higher animals. 

 2 K 2 



