PANCREAS. 



91 



and regards the entire laminated pouch as a 

 more developed form of pancreas than the 

 simple caecum, which we have just described 

 as representing that gland in some of the 

 Gasteropods. 



Vertebrata. Fishes. At the commence- 

 ment of the intestinal canal, close to the 

 pylorus, are found, in most osseous fishes, 

 certain caeca or blind tubes, budding out 

 from the wall of the canal, which from their 

 position have received the name of py/oric 

 appendages, and have been regarded by most 

 anatomists as the analogue of the pancreas in 

 higher animals. In their most simple form 

 that of a single, or two or three short buddings 

 of the intestinal wall, not differing from it in 

 the structures that form them, the analogy 

 would hardly suggest itself, but by gradual 

 steps we are conducted from this simple re- 

 presentative of the organ, through a series of 

 forms of increasing complexity, to a structure 

 bearing some analogy to a conglomerate gland, 

 and at any rate deserving to be considered a 

 special glandular appendage to the alimentary 

 canal ; the casca becoming more and more 

 numerous as we ascend in the scale, and the 

 whole organ more and more concentrated. 

 Thus in the Sandlance (Ammodytes lancea), 

 and Polypterus there is but one pyloric cae- 

 cum; in most of the Labyrinthibranchs, in 

 many species of Amphiprion, in the Angler 

 (Lophins piscatorius), Turbot (Pleuronectes 

 maximus), and Mormyrus there are two ; in 

 the Perch(Percaj/?Mwzafe7zs),the percoid Popes, 

 the Asprodes and Diploprions, three ; in the 

 Miller's Thumb {Coitus gobio), and Father 

 Lasher (Cottus scorpius), from four to nine ; 

 in the Gurnard (Trigla}, from five to nine ; 

 in Scorpasna ancl Holocentrum, six and up- 

 wards ; in the Pilchard (Cupea pilcardus), 

 and Lump-fish (Cyclopterus lumpus), there 

 are fifty, and upwards of fifty in the Tunny 

 {Scomber thynnus) ; in the Cod (Gadus mor- 

 rhua'), there are upwards of 120 : and in the 

 Sturgeon (Aeipenser sturio) and Paddle-fish 

 they cannot be counted.* But the increased 

 complexity, and divergence from the simple 

 caecal form, is not produced only by the 

 greater number of the appendages. As they 

 increase in number, they more and more 

 coalesce at their bases, so that many caeca 

 open by few orifices, and thus the character 

 of the gland is gradually changed, becomes 

 clustered and branched, and passes from the 

 tubular to the racemose type. Thus, in the 

 Pilchard, fifty tubes communicate with the 

 intestine by thirty orifices ; in the Lump-fish 

 the same number by six ; in the Tunny, by 

 five ; in the Sword-fish (Xip/iias g/adius^ 

 there are but two orifices ; and in the Stur- 

 geon, the whole mass of caeca, by continually 

 uniting and re-uniting, come at last to empty 

 themselves into a single tube, equivalent, in 

 fact, to a short and wide pancreatic duct. 



The reasons which have induced anato- 

 mists to regard this organ as the analogue of 

 the pancreas are these. 



* Owen's Lectures on Comparative Anatomy. 



In the first place, the situation ; it is placed 

 at the pyloric extremity of the intestine ; and 

 besides this general similarity in situation, 

 there is this special one, that the hepatic 

 duct has the same relation to it as it has to 

 the pancreas in higher animals. If there is but 

 one orifice, as in the Sturgeon, the hepatic 

 duct opens at its base; if many, at the base of 

 one of them . 



Secondly. If they were merely multiplica- 

 tions of surfaces to which food was to be ex- 

 posed, we should find food getting into them; 

 but this is never the case. I have not been 

 able to detect any alimentary materials in 

 even the largest of them ; their function there- 

 fore must be that of pouring forth some special 

 secretion. 



Again, it is not the way, the particular 

 method, in which surface is multiplied ; that 

 is done by modifications of the lining mem- 

 brane of the intestine, the mucous structures, 

 alone by folds, villi, crypts and not by 

 extension of the whole intestinal wall, mus- 

 cular and sub-mucous, as welL 



Lastly, the filling up of all the intervening 

 stages from simple tube to conglomerate pan- 

 creas goes a great way to prove the essential 

 identity of the extreme forms. 



But what is very remarkable with regard 

 to these appendages is their entire absence in 

 many classes of fish. In all the Abdominal 

 Malacopterygii, except the Salmonidaa and 

 Clupeidae, they are wanting ; in most of the 

 Labroids, Gabioids, Cyprinoids, and Lucioids, 

 they are absent ; in the Apodous Malacop- 

 terygii, in the Lophobranchs and Plectognats 

 there is no trace of them; nor in the genera 

 Antennarius, Malthaeus, and Batrachus In 

 some cases they appear to be wanting in con- 

 sequence of their place being supplied by a 

 more elaborate mucous surface, as in the highly 

 developed stomach of the Anarrhichas, and 

 the glandular palate and long intestine of the 

 Ciir\f(Ci/priniis); in others, their absence seems 

 to be but a part of a general simplicity of the 

 alimentary apparatus, as, for instance, in the 

 Dermopterous fish. In the Eel, where there 

 are no caeca, the mucous membrane at the 

 pylorus suddenly becomes thick, vascular, and 

 spongy, and continues so for about an inch ; 

 and on pressure an abundant secretion may 

 be squeezed out of its wall, of an appearance 

 exactly identical with that found in the 

 pyloric appendages where they are present. 



It is difficult to seize on the law of their 

 existence ; we may, however, say that they 

 are, for the most part, wanting in fish that 

 live on vegetable substances, although there 

 are many similarly circumstanced that are 

 carnivorous and very voracious. Their de- 

 velopment, or their relative size, their number 

 and complication, are probably in proportion 

 to the activity of digestion and rapidity of 

 growth ; the Salmonidae, the Clypeidae and 

 Scomberida?, seem to indicate this : in these 

 last these pyloric caeca exhibit a remarkable 

 complexity. 



In the Turbot (Pleuronectcs maximus) these 

 caeca are seen in their most rudimentary 



