HISTORICAL 17 



Centrechinus . Mortensen holds to the old name of^ Diadema, which Clark 

 abandoned for the "proper" name of^ Centrechinus (Clark, 1925, p. 41; 

 1946, p. 278; Mortensen, 1940, M III, i: 243).' 



e. History of Embryology 



Fertilization (by artificial insemination) of the living sea urchin egg 

 was first described by Derbes in 1847, in Echinus esculentus ; he also 

 described and figured the cleavage and development to the well- 

 developed pluteus of about two weeks; stages described as later than 

 that are probably degenerative and not developmental forms. A little 

 earlier in the same year, 1847, cleavage was described, probably for 

 the first time, from observations made in 1845 on the same species, 

 by von Baer of St. Petersburg; he described the development only to 

 the free-swimming blastula just after hatching. Dufosse (1847), ^^^^ 

 before Derbes, described cleavage, hatching and early development of 

 Echinus esculentus, but this he believed to be entirely radial, and his 

 description is confused and difficult to follow without illustrations. 

 Some years later, a detailed study was made of fertilization and early 

 cleavage of the eggs of the starfish and the sea urchin, Toxopneustes 

 lividus (Paracentrotus?) independently and almost simultaneously by 

 O. Hertwig (1876) and Fol (1877, 1879), ^^^ ^^ Toxopneustes variegatus 

 by Selenka (1878). 



f. The Pluteus 



The name of pluteus for the larval form of some Echinoderms was 

 originated by Johannes Miiller in 1846. He gave the name Pluteus 

 paradoxus (1846 a) to what he thought was a new animal which came 

 from the North Sea near Helgoland. Later in the same year (1846 b), 

 he found this to be the larval form of an Ophiuran, later identified as 

 Ophiura albida (Mortensen, 1921, p. 14). The Latin word pluteus he 

 translated into German as Staffelei or Gestell, and the English have 

 translated the German into easel. The word was chosen because of 

 the resemblance of the larva, turned upside down (as Miiller always 

 drew them) to an easel. "Wir sehen ein Gestell vor uns aus 2 Seiten- 

 leisten, die nach oben convergieren... nach unten divergieren und von 



' The long controversy between Mortensen and H. L. Clark (and others) concerning 

 Diadema vs. Centrechinus was finally settled in November 1953 in favor of Diadema (Inter- 

 national Commission on Zoological Nomenclature, Opinions and Declaration vol. 3, Opinion 

 206). The controversy began with R. T.Jackson in 19 12. 



