1888.] 531 [Jackson. 



In the death of Mr. G-reenleaf, the Boston Society of Natural 

 History has sustained a great loss ; those who were associated with 

 him as officers and members feel it as such a personal grief that 

 they will not soon forget his kindly advice and generous aid. 



The following paper was then presented : 



THE DEVELOPMENT OF THE OYSTER WITH REMARKS 

 ON ALLIED GENERA. 



BY ROBERT T. JACKSON. 



The paper here presented is a preliminary paper on the later de- 

 velopment of the oyster, with studies of allied genera. In the por- 

 tion treating upon oysters, I have entered more into detail than 

 was my first intention, but this seemed necessary in order to make 

 a reasonably clear presentation of the facts. 



Bibliographies of the development, life-history and culture of 

 the oyster, are to be found in the works of Professors Brooks (4) 1 

 and Ryder (21), and Dr. R. Horst (7). A comprehensive essay on 

 the life history of the oyster has been published by Prof. John A. 

 Ryder (25), and many papers exist in the Reports and Bulletins 

 of the United States Fish Commission, from 1880-86 inclusive. 



The investigations were carried on by me as a pupil of Prof. Al- 

 pheus Hyatt, and the main lines of research are similar to those 

 followed by that author in his studies of the development of fossil 

 Cephalopods. An attempt has been made to apply his classifica- 

 tion to the later development of the oyster, and the stages of growth 

 have been named 2 in accordance with his system (13), which was 

 presented before the Society November 16, 1887. 



1 References to papers quoted are referred to in the text by numbers in parentheses, 

 of which a list will be found on p. 548. 



2 It is necessary to anticipate by means of a note a brief description of two names 

 used in the text, in order to make clear their meaning in the first part of the paper. The 

 adult shell of cephalous molluscs has been called the conch or true shell, and the young 

 first formed shell on account of its differences, the protoconch. Similarly the young 

 shell of Dentalium has been named the periconch. The adult double shell of an oyster 

 is believed to be the homologue of the adult single shell of cephalous molluscs, and in 

 view of its double character I suggest for it the name dissoconch (double shell). The 

 first formed shell of an oyster is strikingly different from that which immediately suc- 

 ceeds it, and which is retained throughout the rest of life. It is different in form, histo- 

 logical structure, and covers very different organic soft parts. It is thought to be the 

 homologue of the protoconch of cephalous molluscs and the periconch of Dentalium, 

 and is, therefore, named the prodissoconch (early double shell). The detailed consid- 

 eration of the reasons for this nomenclature is given on pp. 540, 542-543. 



