THE MAIN GROUPS OF ANIMALS. XXVll 



that the animals he once ^ alludes to as popularly called " entrails of the 

 earth " are earth-worms. If so, we have another explanation of his 

 division. For, sad to say, he thought that these were embryonic forms 

 of eels, that is, of animals with red blood. 



The Bloodless animals are in every respect less perfect than the 

 Sanguineous, and inferior to them. They are, as a rule, of smaller* size, 

 and live for a shorter time.' They are colder, as is shown not only by 

 their want of blood,* but also by the almost universal absence of any 

 special provision for refrigeration, such as gills and lungs and brain ; 

 the simple bathing of the surface with_airj)r water sufficing, as a rule,) 

 to temper their small heat.' Another proof of this cold nature is furnished 

 by the immature condition in which they produce their young. None 

 of them deposits a perfect ovum, an ovum, that is, which has attained 

 its full growth ; but if they produce an ovum at all, it is at best an 

 imperfect one, an ovum, that is, that increases in size after it is 

 deposited ; and though this is true of some of the least perfect among 

 the Sanguineous animals, namely, the scaly fishes, it is true of all the 

 Bloodless kinds.^ 



It should be said in explanation of this latter ground of distinction, 

 that the ova of fishes and mollusca, and other animals that lay their 

 eggs in water or damp situations, sometimes increase considerably in 

 size after being deposited. This increase was supposed by Aristotle to 

 be due to actual growth,'' whereas it is in reality attributable to mere 

 imbibition of water. This explanation applies to most of his classes 

 of Bloodless animals, but not to Insects. These he thought produced 

 something even less mature than the imperfect ovum of the water , 

 animal, and to it he gave the name of Scolex. The scolex was distin- 

 guished from the ovum not only by being less mature, but by being 

 metamorphosed as a whole into the perfect animal ; and not, as the 

 true ovum, serving partly for the nourishment of the embryo, partly 

 for its development. It has been supposed from this that Aristotle had 

 in some extraordinary way overlooked the eggs of insects, and fancied 

 that these animals produce primarily grubs or maggots. This, however, 

 was not so. He says that there are two kinds of scolex, one capable of 

 motion, in other words a grub or maggot, the other incapable of motion, 

 and so excessively like an ovum in shape, size, and consistency, as 

 to be indistinguishable from it, excepting by considering its ulterior 

 changes.® The insects which produce the moving scolex or grub are 



^ D. G. ill. II, 24. Aratus also uses the term "entrails of the earth," apparently in 

 reference to earth-worms. 



- H. A. i. 5, 13 ; De Gen. ii. i, 7. ^ pg Long. V. 4, 2. * D. P. ii. 7, 8. 



* Cf. iii. 6, note 3. ' D. G. ii. I, 17, etc. 



' So also Pliny, ix. 74 : " piscium ova in mari crescunt, quredam summa celeritate." 



* D. G. iii. 9, 5. 



