21^ GKNKHAL ORNITHOLOGY. . 



lacteals already described (p. 199), and the uuassimllablo refuse of the food becomes excreineu- 

 titious. 



Cieca (Lat. circus, bliud ; iu the nom. pi. caea; sing, ccecimi). — The " blind guts," .so 

 called because they end in cuh-de-sac, are <jf tw(j kinds. One is the umbilical ccecmn, i>r 

 vitelline caecwm, a rudimentary, or rather vestigial, structure, the remains of the open duct by 

 wlricli the cavity of tlie umbilical vesicle (an embryonic organ) communicated with that of tlie 

 intestinal tract. It is ordinarily not to be noted at all; but it is said by Owen to have been 

 found half an inch long iu the gallinule, an inch iu the bay ibis, and dilated into a sac an inch 

 in diameter in the Apteryx. The structures ordinarily called cceca, or cccca coli, for they are 

 usually paired, are pouches or diverticula whicli set ntf from the intestine proper at tlie junc- 

 tion of the ileum with colon ; but there is nothing in the intestine itself to mark this point, scj. 

 that \i-hen Cceca are absent, as fre(juently happens, no distinction of ileum from colon or rectum 

 is appreciable. No part of the intestinal tract is so variable as the ctecal; so that presence or 

 absence of these appendages furnislies zoological cliaracters uow-a-days taken very commonly 

 into account in framing genera and families. There are no ca-ca, as iu the turkey- 

 buzzard and some pigeons; there is a single small caecum in lierons. From a condition of 

 extremely small size, like little buds upon tlie intestine, ca;ca are found to elongate to extraor- 

 dinary dimensions ; and the large specimens are frequently saccate or clubbed, with slender 

 roots. In geese and swans the ca3ca are a foot long, more or less ; iu some grouse they are 

 said to be a yard long. In the ostrich, the mucous membrane is thrown into a spiral fidd. 

 However developed, the pliysiology of these intestinal appendages is, the detention of food until 

 all its nutritive qualities are absorbed, and increase of the absorbent surface. 



The Cloa'ca (hg. 101, 1 1) or " sewer," very wvll named, is the termination of the bowel, 

 — an oval or gh.ibular enlargement of the rectum, of sulhcieut capacity at least to contain the 

 completely shelled egg. For, not as in placental mammals, the uro-genital and digestive or- 

 gans are behind-hand in tlieir evolution, and do not entirely lose connection with each other. 

 Nor is there in birds any distinct bladder; but a cavity, originally that of the allautois of the 

 embryo, persists iu coninion with that of the intestines, and is tlie cloaca. Such incomplete 

 distinction between the two as there may be, by a fcdding of mucous membrane or partial com- 

 partment of the whole, results in ch)aca proper and urogenital sinus, in which latter are the 

 papillose orifices of the wrefecs, one on each side, from the kidneys; and of the single oviduct 

 (9) or paired sperm-ducts (^), from ovary or testes. The urine of birds not being liquid 

 recpiires no more of a bladder than the sinus furnishes. The same cavity contains the penis of 

 those birds, as the ostricdi and th-ake, which are jirovided with an organ of copulation. A 

 peculiar anal gland, the bursa fabricii (see froutisp.), also opens into the cloaca. Refuse of 

 digestion, the renal excretion, the spermatic secretion, and the product of conception, are dis- 

 charged by a single anal <a'ifice, the two former en masse. 



Being intimately related to dietetic regimen, and so to the habits of birds, the alimi'u- 

 tary canal varies greatly, — '■ even more than my slight sketch shows, — and consequently affords 

 good zoological characters in the details of its construction. But of all the anatomical systems, 

 this is the one most variable as a matter of physiological adaptation (see p. 67). Its char- 

 acters, even when they seem weighty, are therefore peculiarly liable to be fallacious as indices 

 of natural affinities, and must be applied with discreet caution to morphological classification. 

 Such are commonly only (jf generic significance. Thus in pigeons the cfeca and even the gall- 

 bladder may be present or absent in neighboring genera. 



Alimentary Annexes Some of these, as the saUvary glands, have 1>een noticed already. 



Tlie two most important bodies connected with the digestive tract, and properly considered 



