288 CRESSAVP]LL SHEARER. 



1. Introduction, Matkiual, and Methods. 



Our knowledge of the anatomy of Histriobdel 1 a is based 

 on the papers of Van Beneden (1858), Foettinger (1884), and 

 Haswell (1900). Of these, Foettinger's account is the most 

 extensive, while Haswell's paper is perhaps the most valuable. 

 Both accounts contain a more or less detailed description of 

 the internal structure and organisation of the adult. Several 

 years ago I described the presence of solenocytes in con- 

 nection with the nephridia of Dinophilus. This dis- 

 covery rendered it probable that these peculiar structures 

 would also be found in Histriobdella, with which 

 Dinophilus shows many relationships. Moreover, the 

 different description of the nephridial system given by 

 Haswell in Stratiodrilus from that of Foettinger for 

 Histriobdella called for a re-investigation of these organs. 

 For these reasons the present work was begun. I was soon 

 led to undertake a detailed examination of the animal. It is 

 some twenty-five years since the publication of Foettinger's 

 paper, and during this interval the European species of 

 Histriobdella has received no further attention. In the 

 following account I have endeavoured to clear up Foettinger's 

 description of several of the organs. I have had the advan- 

 tage of having made use of the methyl-blue method of intra 

 vitam impregnation, which has proved most valuable. With 

 its use I have experienced no difficulty in determining the 

 number of the nephridia and their relationship to the segments, 

 and to make out new details in their structure quite impos- 

 sible from ordinary sections of fixed material. 



Good methyl-blue^ preparations of the nephridia can be 

 obtained by placing the lobsters bearing the parasites in small 

 tanks of sea-water, to which sufficient blue has been added to 

 colour the water a light shade. It is necessary for the 

 animals to remain in the blue two or three days before it 

 appears in the nephridia. As the blue is rapidly absorbed 

 by the living tissues of the lobster, an additional quantity has 



' This is " soluble blue," and not methylene blue. 



