226 Notes, iv. 5. 



64. There are not sufficient data to determine with certainty what animals correspond 

 to the Holothurias and Sea-lungs of Aristotle. They are above the sponges, inasmuch 

 as they are unattached to the ground ; but resemble them in the want of locomotion 

 {^H. A. i. i) and of sensibility. Very probably, however, A.'s Holothurias are some of 

 the animals still so named. The only difficulty in accepting this is that the Holothurias 

 are most manifestly sensitive ; for when irritated they actually often eject their viscera, 

 or fall into pieces ; neither are they incapable of locomotion. We may, however, 

 suppose that A. was only acquainted with such dead specimens as fishermen brought to 

 him, or as he found stranded on the shore. 



Pliny is so servile a follower of Aristotle, that there can, I think, be no doubt that 

 \as, pulmones marini are the latter's Sea-lungs. Probably some of the larger kinds of 

 Medusae are meant, the smaller kinds being included with Actiniae under the name 

 Acalephse (cf. Note 61). There are a very large number of species of Medusae in the 

 Mediterranean. I cannot understand why S track should take the Sea-lung to be the 

 Sea-hare [Aplysia depilajts). That Medusae of some kind are meant is rendered probable 

 by the name Sea-lung, which is an apposite title for animals that move by alternate 

 expansions and contractions of the body ; a mode of progression still known as 

 Pulmonigrade, and applied to these animals. Secondly, the Medusae not only float 

 on the surface of the sea, but are often phosphorescent, especially when irritated, and 

 these are characters assigned by Pliny to the Pulmones {^Nat. Hist, xxxii. 52). 



55. If they have absolutely no feeling why does A. not only consider them to be animals 

 but even put them above the sponges, to which he ascribes a rudimentary sensibility ? I 

 take it that he does not mean that they are absolutely without feeling ; but that they have 

 very little of it. 



56. A. thought that parasitical plants, such as mistletoe (Z>. G. i. i, 11), were engendered 

 out of the decay of some part of the tree on which they grew. Bacon {^Nat. Hist. § 656, 643) 

 held a very similar opinion. Mistletoe, he says, is an exudation of something **that the 

 tree doth excern and cannot assimilate." 



67. Very probably some kind of Sedum ; and, according to Fraas, Sedum rupestre 

 or amplexicaule. There is an English species, S. Telephium, which has gained the 

 popular name " Livelong " from its persistent vitality after being pulled up from the 

 ground. 



68. Aristotle's Tethya, or Ascidians, are not Tunicata generally, but only the simple 

 solitary Ascidians, which are always sessile. 



69. A. seems here half inclined to remove the Ascidians, which he had before classed 

 with the Echini as peculiar kinds of Testacea, from these latter, and to place them with 

 the Zoophytes, leaving the Echini behind and making them form part of the Turbinata. 

 Similarly he says later on: "Of the Turbinata some have a spiral shell, as the whelks, 

 and some are simply spherical, as the Echini" (iv. 7, 2). A somewhat fuller account 

 of the double-walled sac, with its two orifices, which forms the covering of the Ascidian, 

 is given elsewhere (/^ A. iv. 6). 



By the " septum " I understand the perforated wall that intervenes between the cavity 

 of the pharynx and the atrium ; by the "median partition" I understand the reflection 

 of the lining membrane, or atrial tunic, over the viscera. A. supposes the heart to be here, 

 because the heart should be in a central position (iii. 4, 13), but he does not profess 

 to have made it out by dissection. The " flesh-like substance " is the real body of 

 the animal. As to the statement that the presence of this substance implies sensibility, 

 of. ii. 8, Note 2 ; ii. 10, Note 10. A. was so convinced that the heart, or whatever 

 corresponded to the heart as the centre of life, must be in a central position, that he 



