Notes, iv. 5. 225 



(cf. Note 43) ; for it is on one side only of the circumference, when the body is viewed 

 from above as it lies in either valve. 



48. This passage is unintelligible, and the text probably corrupt. As it stands, we 

 should have to suppose that A. took the central muscular mass of the oyster to be 

 a head. This is very improbable, and has no support from other passages. It is 

 true that in ch. 7 it is said that all Testacea have a head, and that in the Hist. An. 

 (iv. 4, 21) A., lumping univalves with bivalves, says they all have a head, as also 

 horns and mouth, without specifying its position. But he adds that some of their parts 

 can only be seen " in living specimens, and whilst they are in motion ; " that is to 

 say, he could not find a head in the oyster, which is motionless, though he found one 

 in the locomotive univalves, as the limpet. Probably, as he only says that "some of 

 these parts " are not to be found in the motionless kinds, he may have found the 

 mouth of the bivalves, and perhaps may have taken the labial tentacles for horns. 

 This view is confirmed by a passage {H. A. viii. 2, 16) where, after describing the 

 headless sea-anemone as having a mouth, he says it resembles an oyster taken out of 

 its shell. The ovary in this passage is said to be on the upper side ; a little farther 

 back it was said to be on the right side ; an inconsistency, which also seems to point 

 to some corruption of the text. 



49. Cf. Note 2. 



50. The Echini with small ova are those that live in deep water ; the species with large 

 ova are those that live in shallower places. Cf. Note 41. 



51. The spines are really instruments of locomotion, and Agassiz said were the only 

 ones ; but their main function is probably protective, the chief organs of locomotion 

 being the tube-feet, which A. had not noticed either in Echini or star-fishes. 



52. The same idea is elaborated more fully in an admirable passage in the Hist. An 

 (viii. i), 



53. Having considered the Testacea, A. now passes on to those animals that are inter- 

 mediate between these and plants, to such that is as in aftertime were termed zoophytes. 

 In these, he says, locomotion is feeble at best, and often absent, some of them being 

 actually rooted in the soil. Sensibility is also dull, and sometimes scarce a sign of it is 

 detectable. In both of these characters, as also in the absence of any distinct excretory 

 organs, these animals are closely akin to plants. In this group A. reckons Sponges, 

 Holothurias, Sea-lungs, Acalephae, Star-fishes, and " other similar marine creatures." 

 These latter are probably those mentioned in the Hist. An. (iv. 7, 14) ; of which he says 

 he had gathered an imperfect account from fishermen. Among these is one which 

 naturalists have supposed, not improbably, to correspond with Pinnatula ; and another 

 which I take most probably to be Holothuria tremula, which abounds in the Mediterranean. 



At the bottom of the group are the sponges. Ever since A.'s time it has been a 

 disputed question whether these should be reckoned as belonging to the animal or the 

 vegetable kingdom. Physiologists now admit their claim to be considered animals ; but 

 they would reject the evidence which led A. to the same conclusion. " The sponge 

 exhibits some signs of sensation ; for they say there is considerable difficulty in detaching 

 it from the rocks, unless the attempt is made stealthily" {H. A. i. i, 18), and again, " It 

 is said that the sponge possesses sensation. This is a proof of it ; it contracts if it 

 perceives any intention of pulling it off from the rocks, and so renders the task more 

 difficult. It does the same, if the wind and waves are violent, in order that it may not 

 lose its attachment. There are some persons who doubt this, as the natives of Torona " 

 {H. A. V. 16, 5). Modern naturalists seem to be of the same opinion as these natives of 

 Torona. 



15 



