226 ERNST HAECKEL. 



and Enaema (but in any case not with the expressed limits of 

 their author). Ansema or true " bloodless" Metazoa are the 

 Zoophyta and Plathelminthes (Acoelomi). Ensema or true 

 *' blood animals" are, on the other hand, the Coelomati 

 (worms with blood and ccElom), and the four highest animal 

 races arising from these. The former could be defined as 

 Anamaria and the latter as Hcemataria. 



The attempt to employ the number and differentiation of 

 the constituent germ-lamellae, as the fundamental principle 

 of division for the main groups of the animal kingdom, has 

 very recently been twice carried out in different ways by 

 Gustav Jaeger and E. Ray Lankester. The first gives 

 in his suggestive ' Manual of General Zoology ' (1871) a 

 special chapter on the " Principles of the Layers and of the 

 Groups of Layers : Stratography of the Animal Body." 

 Jaeger separates here — L Two-layered animals {'' the lowest 

 multicellular animals"). 2. Three-layered animals (Coelen- 

 terata). 3. Five-layered animals (Enterata or animals with 

 intestines ; our Bilateria, the five higher groups of animals). 

 Praiseworthy as the attempt is, to apply " stratography" in 

 this manner to animal morphology, it must yet be regarded 

 as misleading in details. This becomes at once apparent 

 by comparing Jaeger's explanation (especially §§ 55, 67) with 

 our explanation in the present essay, which has the Gastraea- 

 theory for its basis. Just as little can I concur in details with 

 the attempt of E. R. Lankester (loc. cit., p. 325). He divides 

 the animal kingdom into — 1. Homoblastica, without dif- 

 ferentiated germ-lamellse (Protozoa). 2. Diploblastica (with 

 two germ-lamellae (Coel enterata). 3. Tripoblastica, with 

 three germ-lamellae (the five higher groups, our Bilateria). 



In our own opinion, if a man wished to characterise in this 

 way the main groups of the animal kingdom by the number of 

 the germ-lamellae, he would do much better to separate them 

 into the following four or five sections: — 1. Ablasteria: Animals 

 without germ-lamellae (Pro^02'oa). 2. Diblasteria: Animals 

 with two permanent germ-lamellae {Gastraeadce, Sjjongice, and 

 the lowest Acalephce) . 3. Triblasteria : Animals Avith three 

 germ-lamellae (the bulk of the Acalepha — Hydromedusa, 

 CtenophorcB, Corals). 4. Tetrablasteria : Animals with four 

 germ-lamellae (cuticular nervous and muscular layers, and 

 intestinal muscular and glandular layers). The Bilateria, or 

 the five higher groups of animals collectively. Among these 

 last the Acoelomi (the worms Avithout body-cavity or blood, 

 the Plathelminthes) Avould represent the loAver condition of 

 development, from which the Coelomati (the worms with 

 body-cavity and blood) have subsequently developed them- 



