METAMORPHOSES OF ANIMALS. 129 



Maeroura, before it appears with all the characteristics of 

 the Brachyura. 



i/ 



Embryology furnishes also the best measure of the true 

 affinities existing between animals. I do not mean to say 

 that the affinities of animals can only be ascertained by 

 embryonic investigations ; the history of Zoology shows, 

 on the contrary, that even before the study of the forma- 

 tion and growth of animals had become a distinct branch 

 of Physiology, the general relationship of most animals 

 had already been determined, with a remarkable degree of 

 accuracy, by anatomical investigations. It is nevertheless 

 true, that in some remarkable instances, the knowledge of 

 the embryonic changes of certain animals gave the first 

 clue to their true affinities, while, in other cases, it has 

 furnished a very welcome confirmation of relationships, 

 which, before, might have appeared probable, but were still 

 very problematical. Even Cuvier, for instance, considered 

 the Barnacles as a distinct class, which he placed among 

 Mollusks, under the name of Cirripeds. It was not until 

 Thompson l had shown, what was soon confirmed by Bur- 

 meister and Martin St. Ange, that the young Barnacle 

 has a structure and form identical with that of some of 

 the most common Entomostraca, that their true position 

 in the system of animals could be determined ; when they 

 had to be removed to the class of Crustacea, among the 

 Articulata. The same was the case with the Lernseans, 

 which Cuvier arranged with the Intestinal Worms, and 

 which Nordmann has shown, upon embryological evidence, 

 to belong also to the class of Crustacea. 2 Lamarck asso- 

 ciated the Crinoids with the Polyps, and, though they were 



1 THOMPSON'S Zool. Researches, ganisation, etc., quoted p. 119, n. 1. 

 etc.; BURMEISTER'S Beitriigc, etc.; a NORBMANU'S Micrographische 

 MAKTIN ST. ANGE, Mem. sur For- Beytrilge, q. a. 



K 



