Notes, ill. 3 — 4. • 193 



certain, for it may only mean the trachea, the passage still by no means necessarily 

 in>plies that A. thought there was any communicating channel between trachea and heart. 

 It merely states that the two are connected by bands, and that a passage of air from 

 the windpipe to the heart is somehow possible in some large animals. In order, however, 

 ^ for this to occur, A. by no jneans supposed it necessary that a direct communicating 

 channel should exist, as is sufficiently shown in his description of the lungs : "When the 

 windpipe," he says, "reaches the lung, it divides and subdivides, each division producing 

 smaller anismaller branches, till the whole lung is. permeated by them" (^H. A. i. 16, 13). 

 "There are also ducts (i.e. the pulmonary blood-vessels) which lead from the heart to the 

 lung ; and these also divide and* subdivide, their branches accompanying the branches 

 from the windpipe. But there* is no communication between thd two (ouSeh 5€ iarX Koivbi 

 ' ir6pos). Notwithstanding this, however, air can pass from the former (i.e. l/te bronchial 

 tubes) into th*e latter (i.e. ths pulmonary vessels), owing to the close contact in which the 

 two lie (5jd t^v avvaci^iv), and be transmitted to the heart" {H. A. i. 17, 5). This 

 passage shows that A. not only had a fair knowledge of the anatomy of the lung, but also 

 that he believed the air to pass from the air-passages into the blood-vessels through 

 their unbroken walls, just as we hold the oxygen to do. The trachea then was not- 

 supposed by him to lead directly to the heart, but merely to the lung. As to his state- 

 ment, if it be his statement, that mechanical inflation of the trachea sometimes sends air 

 visibly into the heart, it can only be explained by his having ruptured the parts in his 

 experimental manipulations. 

 10. Cf. ii. 2,, Note 6; 



(Ch. 4.) 1. It" must not be supposed that A. means that the bloodless animjds have 

 none of what we call viscera. For he often mentions the stomach, intestines, and other 

 internal organs of cephalopods, insects, etc. He limits the term viscera to such internal 

 parts as are so coloured as to resemble blood, of which^in fact he- supposes them to be 

 formed (iii. 4, 3 ; iii. 10, 13). As the bloodless animals have merely a fluid analogous to 

 . blood, so they can only have parts analogous to viscera. It is however to be noted that 

 once A. admits of .an exception to this, viz. the liver or mytis of the Cephalopods (iv. 5> 

 Note 13). This he regards as. a viscus, doubtless on account of its dull-red or violet hufe. 



2. Cf. H. A. yi. 3, 2, where it is said that thc.heart in the bird's egg at its first 

 appearance looks like a bloody spot, and palpitates as though endowed with life;. a 

 description which is the origin of the "punctum saliens" of later writers. These 

 minute observations as to the heart in ovum and embryo were made, as we. learn from 

 atiother passage [De Juv. 3, 4), by A. himself, and are sufficient to establish .his fame 

 as an original oliserver. The hfeart is not actually the first part to appear in the embryo, 

 but it is the first to enter actively into its functions, contracting in the bird so early as 

 the second day of incubation, and becoming a few hours later rhythmical in its motions. 



3. Cf. i. 5, Note I. . • 



4. The liver in the mature foetus forms -j^th of the vyhole body ; in the adult it forms 

 only ^th. The heart also is larger proportionately to the whole body in the young 

 embryo (yb-th) than in the mature foetus (T2ijth), and in the foetus than in adult 

 man (ilijth). In infancy again the lungs are .of a brightish colour, "which might.be 

 compared to Hood froth ; but as life advances they become darker, mottled with spots, 

 patches, etc." <Zl. Quain's Anat. Wi,^. 



5. In calling the heart the origin or centre of the vessels, A. implies two distinct 

 things : firstly, that it is the place where the blood is made ; and, secondly, the place 

 whence the blood, when thus made, is propelled into the vessels, blood going from it, 

 but none returning to it. 



13 



