406 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. . 



An aqueous solution of c'orrosive sublimate or corrosive acetic has also been employed with 

 great advantage, in that it fixes the tissues so completely that on decalcification there is little or 

 no alteration in the relationships oi the different organs. It is nuich superior to formol or alco- 

 hol in tills respect. Before conmiencing the decalcification of material which has been in alcohol 

 oi- formol for some time. I have often found it advantageous fo pass it through a solution of cor- 

 rosive sul)limate. 



Decalcification has generally been performed in a weak solution of hydrochloric or nitric acid, 

 after the material has been thoroughly hardened. The acid is added drop Ijy drop to a fragment 

 of the coral still in the preservative Huid in sufficient quantities to maintain a slight efl'ei-vescence. 

 From one to two days are retpiired for the decalcification of small pieces of jjorous corals, such 

 as Madrepora and Porites, whereas the decalcification of dense coralla, like those of Sidermtra&a 

 and Oculina, occupies three or four days. Where it has been desirable to carry out the decalci- 

 fication with special care, as in investigations of the calicoldast layer and skeletal matrix, very 

 weak solutions of acetic and chromic acids have been employed, and then the process requires a 

 nuicli longer period. When, as is usually the case, perforating algal matter occui-s within the 

 skeleton, it is advisable to remove this from time to time, so as to keep a fresh calcareous surface 

 exposed. 



If decalcification of properly fixed material be slowly carried out, there is little or no dis- 

 tur1)ance of the primary relationships of the soft parts. After a few attempts, I concluded that 

 nothing was to be gained by making preparations of the hard and soft parts in situ, such as are 

 obtained 113^ emljedding fragments of a colony in Canada balsam and then grinding down to micro- 

 scojjic thinness. All the figures of the sections are, so far as concerns the relationships of the 

 soft and hard parts, actual reproductions of camera lucida drawings. The irregularity in outline 

 of many of the septal invaginations can be understood when one considei's how generally the 

 septa are provided with spines or graiudes. 



Much of the work has been carried .out while in Jamaica, and the remainder during the 

 academical year 1899-1900, in Professor Brooks's biological laboratory at the Johns Hopkins Uni- 

 versitv." jNIy thanks are due to Prof. W. K. Brooks for many valual)le suggestions and much 

 kindly interest during my stay in Baltimore; also to Prof. A. C. Haddon, of the Royal College 

 of Science, Ireland, and Prof. G. B. Howes, of the Royal College of Science, London, for much 

 assistance and encouragement from time to time during the progress of the work. 1 am inde))ted 

 to Rear Admiral (then (!!ommodore) H. N. Henderson for generously afi'ording me facilities for 

 collecting in the waters around Port Royal and the Cays beyond. Mr. T. Wayland Vaughan, of 

 the United States Greological Survey, has assisted me in the specific determinations. In his recent 

 account of the fossil coi'als from Cura(;ao (1901), and also of the stony corals of the Porto Rican 

 waters, Mr. Vaughan (1901r/) has dealt with the difficult subject of the synonymy of West Indian 

 corals. 



The papcM- is divided into two parts. The first is devoted to a more general description of 

 the external characters and morphology of coral polyps, so far as the material available will 

 permit, and the second to a description of the external characters and internal anatomy of certain 

 representative species. To the former a few notes on larvie and postlarval development are 

 added, which, although incomplete, assist in an understanding of the significance of many of the 

 adult features. In a large measure, also, 1 have carried out comparisons with the better-known 

 Actiniaria. The polyps of the two groups are so closely alike that a knowledge of the characters 

 in the one often assists in throwing light upon conditions in the other. In the second or system- 

 atic part, I have ventured to indicate some of the broader lines of relationships among the Madre- 

 poraria, suggested l)y the new facts obtained, and have attempted for the first time generic 

 diagnoses in terms of the polyp. It will be understood that where generic characteristics are 

 given they have refex'ence only to the representatives here studied. The isolation under which the 



" Since the presentation of tlie paper the studies have been continued, and results of some importance obtained, 

 whicli amplify fortaiii of those here given, particuhirly those on growth b)' gemmation and fissiparity. Tliey are 

 referred to in foot-notes on various pages. 



