44 Thomas Henry Huxley 



consists of two layers of cells, in fact of two foundation- 

 membranes, one forming specially the wall of the future 

 digestive canal, the other forming the most external 

 portion of the future animal. In these days nothing 

 could have seemed a remoter or more unlikely com- 

 parison than one instituted between Medusas and the 

 embryonic stages of back-boned animals. But Huxley 

 made it, not allowing the evidence brought before his 

 reason to be swamped by preconceived ideas. At the 

 time he did no more than to make the comparison. It 

 was much later that the full importance of it became 

 known, when more extended work on the embryolog}- 

 of vertebrates and of the different groups of the inverte- 

 brates had made it plain that the two foundation-mem- 

 branes of Huxley occur in all animals from the Medusae 

 up to man. In the group of Coelenterata the organisa- 

 tion remains throughout life as nothing more than a 

 folding in and folding out of these membranes. The 

 early stages of all the higher animals similarly consist 

 of complications of the two membranes; but later on 

 there is added to them a third membrane. Thus the 

 group that Huxley gathered together comprises those 

 animals that as adults remain in a condition of devel- 

 opment which is passed through in the embryonic life 

 of all higher animals. The immense importance of 

 this conclusion becomes plain, and the conclusion itself 

 seems obvious, when seen in the light of the doctrine 

 of descent. The group of Ccelenterata represents a sur- 

 viving, older condition in the evolution of animals. 

 Huxley himself, when on the Rattlesnake, regarded 

 evolution only as a vague metaphysical dream, and he 

 made the comparison which has been described without 

 any afterthought of what it implied. In this we have 

 the earliest authentic instance of the peculiar integrity 



