726 REMINISCENCES OF HUXLEY. 



notion that o-roups of animals should l)o arranjrod in an asr-ondin^ or 

 (h'sconding scries, and he fully proved the existence of three divert^ent 

 types — Vertebrata, Mollusca, and Articulata. Some of the multitude 

 of animals lowm* or less specialized than these he j^roupt^d by mistake 

 alonw- with Mollusca or Articulata. while all the rest he threw into a 

 fourth class, which he called Radiata. It was evident that this type 

 was fai- less clearly defined than the three hioher types. In fact, it 

 was open to the same kind of ol)jection that used to be efi'ectively urged 

 aj'-ainst Max Muller's so-called Turanian group of languages; it was 

 mei-ely a negation. Kadiata were simply animals that were neither 

 .Vrticulata nor Mollusca nor Vertebrata; in short, the>' were a motley 

 multitude, about which there was a prevailing confusion of ideas at the 

 time when young Huxley l)egan the study of jellyfish. 



We all know Jiow it wtis the work of the great Esthonian embr3^o- 

 logist, Baer, that turned Herbert Spencer toward his discovery of the 

 law of evolution. It is therefore doubly interesting to know that in 

 these earl}' studies llu.xley also profited by his knowledge of Baer's 

 methods and results. It all tended toward a theory of evolution, 

 although Baer himself never got so far as evolution in the modern 

 sense; and as for Huxley, when he studied Medusie, he was not con- 

 cerned with any general theory whatever, but only with putting into 

 shape what he saw. 



And what he saw was that throughout their development the Me- 

 fhisae consist of two foundation membranes or delicate we))-like tissues 

 of cells — one forming the outer integument.the other doing duty as stom- 

 ach lining — and that there was no true l)ody cavit}' with blood vessels. 

 I le showed that groups apparently (juite dissimilar, such as the hydroid 

 and sertularian i)olyps, the Physophorida* and sea anemones, are con- 

 structed upon the same plan; and so he built up his famous group of 

 Coelenterata, or animals with onl}^ a stomach cavity, as contrastcnl with 

 all higher organisms, which might l)e called Cwloraata, or animals with 

 a true body cavity containing a stomach with other viscera and blood ves- 

 sels. In all Oelomata, from the worm up to man, there is a third foun- 

 diition membrane. Thus the Cuvierian group of Radiata was broken up, 

 and the way was prepared for this far more profound and true arrange- 

 ment: (1) Protozoa, such as the anueba and sponges, in which there is 

 no distinct separation of parts performing different functions; (2) Coe- 

 lenterata, in which there is a simple differentiation between the inside 

 which accumidates energy and the outside which expends it; and (3) 

 Coelomata, in which the inside contains a more or less elaborate nys- 

 tem of distinct organs devoted to nutrition and reproduction, while 

 the outside is more or less differentiated into limbs and sense organs 

 for interaction with the outer world. Though not yet an evolutionist, 

 Huxley could not repress the prophetic thought that Coelenterata are 

 ancient survivals, representing a stage through which higher animal 

 t3'pes must once have passed. 



