INTRODUCTION 



EVER since Joh. Miiller about seventy years ago published his 

 celebrated studies on the Echinoderm larvae, showing such un- 

 expected richness of forms to exist among them and making known in 

 the main features their wonderful metamorphosis, these larvae have been 

 among the favourite objects of zoological research. The study of the 

 larval forms themselves, the differentiation of the original simple larval 

 type into the many highly specialized or even quite extreme forms (e. g. 

 Auricularia nudibranchiata or Echinopluteus transversus), tracing the mor- 

 phological transformation of the different parts of the larval body (so 

 masterly done already by Joh. Miiller) or of the supporting skeleton makes 

 in itself quite a fascinating subject. The metamorphosis of the bilateral, 

 free-swimming larva into the radial, more or less sedentary, adult — a 

 metamorphosis no less striking than that of a caterpillar into a butterfly 

 (indeed, the Echinoderm metamorphosis has been characterized as the 

 most remarkable ontogenetic change in the animal kingdom) — presents 

 a number of interesting problems. Then the Echinoderm larvae have 

 proved to be exceptionally good objects for experimental embryological 

 studies, for experimental hybridization and for heredity studies. No 

 wonder that an extensive htterature has arisen on forms presenting so 

 many points of interest. 



The significance of the pelagic larvae for the study of geographical 

 distribution was pointed out in the author's work „Die Echinodermen- 

 larven der Plankton-Expedition" (1898. p. 108), and this was in the 

 author's mind when, speaking of the relation between the East African 

 and the West Indian Echinoid fauna i), the desirability of studying the 

 development of the forms common to both regions, as, upon the whole, 

 that of tropical Echinoderms in general, was emphasized, this being almost 

 a terra incognita, „an ample field of most promising research". 



1) Th. Mortensen. On some "West Indian Echinoids. Bull. U. S. Nat. Museum. 74. 1910. 

 p. 25. 



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