THE GASTRAEA-THEORY, ETC. 225 



as egg- animals (Ovularia), because they possess a shape cor- 

 responding to the simplest (nucleus-containing) egg-cell or 

 the egg-cytode (without nucleus). With these must also be 

 reckoned the planula representing animal forms (Plan^ada), 

 and, finally, the Grcgarinie, the Acinetfe^ and the true ciliated 

 Infusoria (Ciliata). 



The second main division of the animal kingdom is com- 

 posed of the six higher stem-groups, which are all derived 

 from the common stem-form of the Gastraea. We class them 

 together as germ-lamellar animals, Metazoa (or Blastozoa), 

 or animals with an intestine (Gastrozoa) . In all these animals, 

 from the sponges up to the Vertebrata, the body always 

 originally develops itself from two primary germ-lamellffi, the 

 animal exoderm, and the vegetative endoderm. The latter 

 always encloses a true intestinal cavity with a mouth-opening.^ 

 Therefore the body has the form-value of a morphon of the 

 third order, a true person, or is composed of several persons, 

 and is then an individual form of the fourth order, a 

 stock ('Biology of the Calcareous Sponges,' p. 103, &c.). 

 All these germ-lamellar animals possess at least two different 

 systems of organs, namely, the dermal system (the covering 

 of the outer germ-lamellae with its derivatives) and the 

 intestinal system (the intestinal outfolding of the inner 

 germ-lamella with its derivatives). 



In further classifying the Metazoa, we may, in the first 

 place, advantageously make use of three different principles of 

 division — 1. The want or possession of the coclom, 2. The 

 different number of the secondary germ-lamella?. 3. The 

 radial or bilateral fundamental form. 



If we would attach a principal importance to the coelom 

 and the vascular or blood system depending upon it, then the 

 main division Metazoa divides next into two distinct groups ; 

 on the one side the lower germ-lamellar animals without 

 coelom or hoemolymph ; Zoophyta and Acoelomi (Plathelmin- 

 thes) ; on the other the higher Metazoa with coelom and heemo- 

 lymph ; the Coelomati and the four highest groups of animals 

 springing from these — Echinodermata, Arthropoda, Mollusca, 

 and Vertebrata {vide the ' Biology of Calcareous Sponges,' 

 pp. 467, 468). We could adopt for these two groups the 

 original terms, in their strictest sense, of Aristotle, Ansema 



' The few animals araoug the Blastozoa which are without an intestine, 

 the Cestoda and Acanthocephala, eanuot be considered here as an exception, 

 as they have apparently lost the intestine in consequence of their parasitic 

 habits, and originally sprung from worms provided with an intestine. This 

 follows, unquestionably, from their comparative anatomy and ontogenesis.— 

 Fide ' General Morphology,' vol. ii, p. Ixxx. 



