3o6 XOTES. 



Note XVL, Chapter TV., p. 221. 



THE DEVELOPMENT OF THE CRAYFISH. 



The remark made in the last note applies still more strongly to tlie 

 history of the development of the crayfish. Notwithstanding the mas- 

 terly memoir of Rathke, which constitutes the foundation of all our 

 knowledge on this subject ; the subsequent investigations of Lereboullet ; 

 and the still more recent careful and exhaustive works of Reichenbach 

 and Bobretsky, a great many points require further investigation. In 

 all its most important features I have reason to believe that the accomit 

 of the process of development given in the text, is correct. 



Note XVII., Chapter VI., p. 207. 



PARASITES OF CRAYFISHES. 



In France and Germany crayfishes (apparently, however, only 

 A. nohilis) are infested by parasites, belonging to the genus Branchio- 

 Idella. These are minute, flattened, vermiform animals, somewhat like 

 small leeches, from one-half to one-third of an inch in length, which 

 attach themselves to the under side of the abdomen {B. 2Mrasitica), or 

 to the gills (B. astaci), and live on the blood and on the eggs of the 

 crayfish. A full account of this parasite, with reference to the literature 

 of the subject, is given by Dormer (" Ueber die Gattuug Branchio- 

 bdella : " Zeitschrift fiir Wiss. Zoologie, XV. 1865). According to Gay. a 

 similar parasite is found on the Chilian crayfish. I have never met with 

 it on the English crayfish. The Lobster has a somewhat similar parasite, 

 Histriohddla. Girard, in the paper cited in the Bibliography, gives a 

 curious account of the manner in which the little lamellibranchiate 

 mollusk, Cyclas fontinalis, shuts the ends of the ambulatory limbs of 

 crayfishes which inhabit the same waters, between its valves, so that the 

 crayfish resembles a cat in walnut shells, and the pinched ends of the 

 limbs become eroded and mutilated. 



