INTRODUCTION. 



During a stay on the island of Tobago, British West Indies, in March 

 and April, 1916, with the expedition of the Carnegie Institution of Wash- 

 ington, I succeeded in rearing the young of the Crinoid Tropiometra carinata 

 from the egg up to the fixed stage and also in keeping the Pentacrinoids 

 aUve for some time, until the appearance of the first radials. Since our 

 previous knowledge of the embryological development of Crinoids is based 

 exclusively on the European species, Antedon bifida, A. mediterranea, and A. 

 adriatica, all being at least very closely related, it is of no small interest to 

 become acquainted with the embryology of a species belonging to another 

 genus, and even to another family. To generalize from a single type and 

 apply the facts to a whole order is dangerous. It is only through the study 

 of the embryology of different types that we can form a true judgment as to 

 which features are of general and which only of specific value in the develop- 

 mental history of this and other groups of echinoderms. Although it would 

 be more interesting and important to have the embryology of some stalked 

 Crinoid worked out, I think the facts made known through the present study 

 will be found to be of some value and to represent progress. 



I have included in this memoir a report on the development of some 

 other Crinoids, namely, Compsometra serrata (A. H. Clark), from Japan, 

 Florometra serratissima (A. H. Clark), from the Strait of Georgia, Isometra 

 vivipara Mortensen, Notocrinus virilis Mortensen, and Thaumatometra nutrix 

 Mortensen, all three from the Antarctic Sea. As to the two first named, 

 I succeeded in getting material for the study of their development during 

 my voyage in the Pacific in 1914-15. For the three other species I am 

 indebted to Professor O. Nordenskjold, of Gothenburg, who sent to me the 

 whole of the collection of Crinoids made by the Swedish Antarctic Expedition 

 (1901-03), inclucUng the "Antedon hirsuta" of Dr. K. A. Andersson {Isometra 

 vivipara), the first truly viviparous Crinoid known. Of this species, material 

 was found for the study of the whole development from the egg until the 

 Pentacrinoid is ready to detach itself from the stalk. Then I had the great 

 pleasure of finding in this material two more new viviparous forms, namely, 

 Notocrinus virilis and Thaumatometra nutrix.^ Although only some larval 

 stages were found of the former species and the Pentacrinoid stages of the 

 latter, several important facts were disclosed thereby. 



'Th. Mortensen: Notocrinus tirilis n. r., n. sp., a new viviparous Crinoid from the Antarctic Sea. 

 Preliminary notice, Vid. Medd. Dansk Naturh. Foren. Kobenliavn, 68, 1917, p. 205. 



The Crinoidea of the Swedish Antarctic Expedition. Wiss. Ergebn. d. Schwed. SUdpolar-Eiped. 



1901-1903, vol. VI, 1917, platea i-v. 



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