OB ANIMALS WITHOUT BLOOD. 217 



minute apertures of the sponge and ejected through the 

 larger passages, now called oscules, that this error was fully 

 corrected.* 



Sea-anemones and medusae were included by Aristotle 

 under the name Akalephe or Knide, each meaning a nettle. 

 He says that this group of animals is peculiar, and that 

 some live attached to rocks, while others are free.t Speak 

 ing of the sea-anemones, he says that they have a central 

 mouth and that they seize, as it were by a hand, small 

 fishes that come in their way, and, probably referring more 

 particularly to medusae, he says that they can sting so 

 much that the flesh is made to swell.! 



Aristotle s Ostrakoderma, one of his four great classes 

 of Anaima, included molluscs (other than cephalopods), 

 echinoderms, and ascidians, the last two being peculiar kinds 

 of Ostrakoderma. The typical animals of this class were 

 snails and oysters, having their internal parts fleshy, but 

 their external parts hard and brittle, jj 



The main characteristics of the whelk (Buccinum) are 

 clearly stated by Aristotle. He calls it Keryx, and states 

 that its shell is spiral and rough, 11 and that it has a powerful 

 proboscis,** and he also notices its operculum and its egg 

 capsules, ft He erroneously believed that the proboscis was 

 the effective means used by the whelk in boring through 

 shells and other hard substances, whereas it is the radula. 



The most interesting gastropods described by Aristotle 

 are his Porphurai, which included Murex brandaris, in 

 particular, M. trunculus, and some species of Purpura. He 

 says that the Porphura has a spiral shell and a powerful 

 proboscis.il This mollusc makes, he says, the so-called 

 honeycomb (egg capsule), which is not, however, hollowed 

 out like a honeycomb, but composed of what may be com 

 pared to the white pods of certain plants; Porphurai, he adds, 

 are not produced from the honeycomb, which is of the 

 nature of excreta. He also refers to the operculum. || || As 

 in the case of the Keryx, he erroneously believed that the 

 proboscis of Porphura was used for boring hard substances. 



It is well known that the famous Tyrian dye was prepared 



* &quot; Observations, &c., on the Sponge,&quot; Edinburgh Pliilospli. Journ., 

 vol. xiv. 1826, pp. 117-9. 



f E. A. iv. c. 6, ss. 4 and 5. J Ibid. iv. c. 6, s. 4. 



P. A. iv. c. 5, 680a. || H. A. iv. c. 1, s. 2. 



&amp;lt;I Ibid. iv. c, 4, ss. 1 and 3. ** Ibid. iv. c. 4, s. 8. 



ft Ibid. v. c. 13, ss. 1 and 7, JJ Ibid. iv. c. 4, ss. 1 and 8, 



Ibid, v, c. 13, s. 1. || |l Ibid. v. c. 13, s. 7. 



