SOME SPECIFIC CHARACTERS 



23 



side of the " head " a very minute gill far away from the 

 others and previously unknown. The demonstrator in 

 charge of the class refused even to look at her discovery. 

 So she confirmed it by examining three other specimens 

 — made drawings of the tiny 

 branched gill (as shown in Fig. 

 33) and their position, and sent 

 them to me in London. It was 

 at once clear that she had dis- 

 covered in this much studied 

 little animal a very interesting 

 pair of gills (right and left) — 

 unknown to Huxley and the rest 

 of the zoological world. She 

 proceeded to examine specimens 

 of A. fluviatilis from various 

 rivers of Germany and France 

 and always found the new gill- 

 plume. She also showed (I 

 supplied her with specimens at 

 the Natural History Museum) 

 that it was, on the other hand, 

 absent from A. leptodactylus, 

 A. pallipes, and all the foreign 

 species (some from Asia) which 

 are known, and she published 

 an illustrated account of it in 

 the "Quarterly Journal of 

 Microscopical Science." This 



tiny gill-plume is placed very far forward on each side 

 of the body, the farthest point forward at which any 

 gill-plume is found in any kind of prawn, shrimp or 

 lobster, namely in the region where the first pair of jaw- 

 legs is attached, so that there are three empty spaces 

 between it and the rudimentary gill over the fifth pair of 



Fig. 33. — The rudimentary 

 gill-plume of a crayfish from 

 that part of the body-wall 

 to which the first pair of 

 jaw-legs (maxillipedes) is 

 articulated. Found in the 

 red -footed crayfish (Astacus 

 fluviatilis) but in no other 

 species of Astacus. It is 

 one-fifteenth of an inch long. 

 Drawn by Miss Margery 

 Moseley in 1904. (" Quart. 

 Journal of Microscopical 

 Science," vol. 26 (1904-5).) 



