• Notes, ii. 9. 171 



of other vertebrata. * This makes them more brittle, which is what A. must mean by 

 calling them weaker. 



7. Here A. speaks of the bones of the smaller serpents as made of fish-spine ; else- 

 where (i v. II, 17) he says they are cartilaginous. In reality however the proportion of 

 inorganic matter in a snake's bones is very high, nearly as high as in the bones of birds ; 

 and this it is which gives so beautiful a whiteness and compact a look to a snake's 

 skeleton. I can find no confirmation of A. 's statement that there is a difference between 

 the bones of small and of large serpents. The only large ophidian he can possibly 

 have seen was the Coluber elaphis, which sometimes attains a length of six feet. His 

 information as to other large serpents was simply derived from Such "traveller's tales" 

 as that given at H. A. viii. 28, 10, 



8. Cf. iv. 13, Notes i and 33. The skin of the fishes called Selachia by A. is studded 

 with numerous tubercles, granules, or spines, of bony matter ; a peculiarity designated 

 as " placoid " by modern ichthyologists. ' • 



9. . It has been a matter of question, whether the credit of being the first to put forth 

 the law "of organic equivalents should be assigned to Geoffrey St. Hilaire or to Goethe ; 

 the former of whom spoke of it as " la Iqi de balancenlent organique," while tl^^ latter 

 expressed it in these terms, "Nature must save in one part in ordei: to spend in another." . 

 As a matter of fact, the law, whfether true or false, is perfectly recognised by Aristotle, 

 and is used by him over and over again in explanation of morphological phenomena. 

 We have" already had in this book one instance of this, when the inverse relation of fat 

 and the generative secretions was mentioned (cf. ii. 5, Note 9), and we shall come to 

 numerous others. Thus, for instance, is explained (ii. 14, Note 4) the coincidence of 

 long hair and short fail; thus also (iii. 2, Note 19) the want of upper front teeth in 

 horned animals ; thus again (iv. 9, Note 12) the great length of the arms in cephalopods 

 with a short body, and their comparative shortness when the body is long, etc. , etc. 



10, Seeing how much attention A. gave to development, it is strange that he should 

 not have noticed that the osseous is preceded by a cartilaginous framework. Had he 

 done so, he would certainly have cited th© fact here, in support of his statement of the 

 essential identity of the two substances. 



11. See also Hippocrates (Kilhn's ed. i. 319). When cartilage is fractured, •reunion 

 may be effected by fibrous or by calcareous tissue, but never by true cartitage ; whereas 

 when bone is fractured, reunion is effected by true osseous tissue. Frantzius and Lewes 

 find in this grounds for attacking the statement in the text. But in reality A. says 

 nothing about reunion of broken parts, and neither he nor Hippocrates can have been 

 ignorant of the common facts of the mending of a broken bone. • What is said is that 

 a piece of cartilage or of bone, if once excised, is never regenerated ; and though this 

 is not actually true, it is what every physiologist believed to be so till comparatively 

 a short time ago. The statement is founded partly on surgical experience, partly on 

 observations of mutilated animals. When a portion of bone is removed by the surgeon, 

 It is not regenerated unless the periosteum be left. This was unknown till Duhamel's 

 time, though Hippocrates was near it when he said, "An extensive fracturfc is less 



■formidable if the periosteum be sound" (iii. 369), and A. also when he said, "A bone 

 becomes necrosed, if stripped bare of its membrane" {H. A. iiL 13, 2). No effort being 

 made by the ancients to preserve the periosteum, removal of bone was never followed 

 by regeneration. That excised cartilage is never replaced is still the general belief ; but 

 Legros and Peyraud" have recently showTi that regeneration can occur also in this tissue 

 if the perichondrium be preserved {ViixJumfs Jahresb. 1869, -p. 143). As to mutilated' 

 animals, it was known to A. i^H. A. ii. 17, 24) that when a lizard's tail is cut off, the 



