ORAL APPENDAGES OF MARINE ISOPODA. 67 



I have much pleasure in here expressing my thanks to the authorities of 

 the U.S. Natioual Museum, Washington, for specimens of many of the 

 species examined ; to Professor D'Arcy W. Thompson for examples of 

 Mesidotea sabini (Kroyer) ; to Professor Ohas. Chilton for various New 

 Zealand species ; to Mr. Keppel H. Barnard for many South African species ; 

 and to Mr. Walter H, Baker for South Australian species. 



Under the different species the more important references have been given, 

 but no attempt has been made to give the complete list of synonyms or 

 references. 



II. Method of Preparation. 



Most of the errors in previously published figures and descriptions of the 

 oral appendages of the Idoteidaj are due to the fact that the different 

 segments, joints, spines, etc. are not always shown, and this has no doubt 

 partly arisen owing to the appendages having been imperfectly prepared for 

 microscopical examination. 



The old method of boiling or even soaking in a solution of caustic soda is 

 unsatisfactory, as frequently the different parts become separated from one 

 another and also become altered in form to a greater or lesser degree. 



After considerable experimentation, f think I have at last arrived at a 

 method that is thoroughly satisfactory. So far as I am aware, the details 

 have not previously been published ; it therefore seems desirable to describe 

 the method in detail. 



The original idea of treating chitin as described below is Professor J. 0. 

 Irvine's, who adopted it in a research on the chemical nature of chitin 

 derived from different sources*'. He has very kindly given me the essential 

 details of the process, and with these I have made numerous experiments 

 and modifications, ultimately evolving the following process for clearing and 

 staining small chitinous objects, such as the appendages and other parts of 

 (he exoskeleton of Crustacea. 



All the material dealt with had previously been preserved in alcohol. 

 Upon removing the appendage or particular part to be studied, it was placed 

 in a small quantity of a 15 °/ n solution of HOI, and there allowed to remain 

 for a period varying from twenty minutes to three hours, according to the 

 size and thickness of the object. The receptacles used for containino- the 

 specimens and fluids were small flat glass dishes 39 x 39 x 9 mm. with a 

 circular concavity 5 mm. in depth, and covered with a square of glass. Upon 

 removing ih" specimen from the HC1 it was well washed in distilled water 

 and then transferred to a 5 % solution of caustic soda, in which it was 

 allowed to remain for one to three hours, and then placed in a 4 °/ solution 

 of sodium permanganate for a period varying from thirty minutes to two 



' Trans. Chem. Soc. Loud. vol. xcv. (1909) pp. 564-570. 



6* 



