90 



On the Classification of Animals 



(which, it is to be noted, are multiples of 2 and 3), 4 being 

 the number for the class of Medusss, and both 4 and 6 occurring 

 in that of Polyps. But if the number of rays is 5, as in the 

 highest of Kadiates, the Echinoderms, while examples of perfect 

 symmetry occur, there are many cases of unsymmetrical forms 

 (as in the Spatangi) in which the Radiate type seems to tend to 

 emerge from phytoid towards true animal-like forms. In the regu- 

 larly radiate, the mouth is central or very nearly so, while in the 

 Spatangi, there is something of the fore-and-aft form of the animal. 



Among species under the true animal-type there are forms 

 showing an approximation to the central position which the mouth 

 has in Radiates. In a Limulus, for example, the mouth-aperture 

 is only one-half less remote from the anterior margin of the body 

 than from the posterior (base of caudal spine). The Limuli are 

 extreme in ampUficative decephalization and in lowness of grade. 

 Under the multiplicative method also, there is something similar 

 in Worms and Myriapods. The head is here strictly at the ante- 

 rior extremity ; but the cephalic force has so feeble control, that 

 joints multiply behind; and in the lowest of Worms, each sepa- 

 rate segment is nearly equal in all functions to the cephalic 

 segment. Moreover, in the embryological development of an An- 

 nelid, the first segment (with its pair of appendages) that is 

 formed after the appearance of the head is not the anterior one 

 close to the head, but the eighth (or one near this) ; and from this 

 point the rings form in succession posteriorly, and also towards 

 it from the head ; as if, in these muWplicate species, there was a 

 secondary centre of force distant from tlie front which preponderates 

 over the primary one. 



This method viewed on the ascending grade is the holozoic (from 

 oXog all, and Jwoi/ animal) ; it is exhibited in a rise from the plant- 

 like type to the true animal-like type. 



E. Postural. 



11. Postural. — Exhibited in an increasing proneness in the 

 position of the nervous system — the extremes being verticality in 

 Man, and horizontality in the Fish. 



F. Embryological. 



12. Prematurative. — Exhibited in precocity of young or larves. 

 Thus, the chicken, as soon as born, runs about and seeks its 



own food, while the young of those Birds which belong to the 

 superior group, — the true flying Birds — remain helpless until able 

 to fly; a fact recognised in Bonaparte's classification of Birds. 

 So the young colt or calf (Herbivorous) is on its legs almost as 

 soon as born ; but the young kitten (Carnivorous, and higher in 

 type) is for a considerable time helpless. 



Prematurity has often been recognised as evidence of low 



