486 MAYOR. 



1. Introduction. 



Interest has been re-awakened of recent years in the development of 

 the Hexacorallidae by the papers of Duerden (:04), who has estab- 

 lished the order of development of the mesenteries in the larva and 

 of the septa in the attached polyp. As regards the larval develop- 

 ment his work agrees in the main with that of Wilson ('88) on 

 Manicina areolata. In the skeleton Duerden is the first to find bilat- 

 eral symmetry in the order of development of the primary exosepta. 

 Our knowledge of the development of coral larvae is in the main 

 confined to four species; Astroides calycidaris (Lacaze-Duthiers '73); 

 Manicina areolata (Wilson '88) ; Caryophyllia cyathns (Von Koch '97) 

 and Siderastrea radians (Duerden :04). The early development of 

 the skeleton has been studied in Astroides calycidaris by Lacaze- 

 Duthiers ('73), in CaryojihyUia cyathus by Von Koch ('97), in Caryo- 

 phyllia clavns, C. smithii and Balanophyllia regia by Lacaze-Duthiers 

 ('97) and in Siderastrea radians by Duerden (:04). 



In 1907 the writer went to the Bermuda Biological Station for the 

 purpose of studying the development of a recent coral. ^ He was 

 fortunate enough to find the common "hat" or "shade" coral, Agari- 

 cia fragilis, breeding and was able to rear the larvae. 



As the development of the primary mesenteries of the larvae of 

 corals has been worked out in comparatively few cases and a study of 

 the soft parts seemed a necessary prelude to a study of the skeleton, 

 free swimming larvae have been studied both in the living state and 

 in paraffin sections. These observations form the first part of the 

 paper. The writer was not very successful in rearing the young polyps. 

 In consequence only a few skeletons were obtained. The second part 

 of the paper is devoted to a description and discussion of these young 

 skeletons. 



2 The writer wishes to express his indebtedness to Dr. E. L. Mark for kind 

 assistance and criticism while at the Biological Station and later in the Zoo- 

 logical Laboratory of Harvard University. 



