< Page:Popular Science Monthly Volume 16.djvu
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THE POPULAR SCIENCE MONTHLY.

It will probably not be welcome news to some of our readers that the English crayfish is in all probability not entitled to the current title of Astacus fluviatilis. This name appears to belong to a larger species, sometimes called A. nobilis, hardly distinguishable from the

Fig. 5.—Astacus fluviatilis. In A, the gills, exposed by the removal of the branchiostegite, are seen in their natural position; in B. the podobranchiæ are removed, and the anterior set of arthrobranchiæ turned downward (x 2): 1. eye-stalk; 2. antennule: 3. antenna; 4. mandible; 6. scaphognathite; 7, first maxillipede; in B the epipodite. to which the line points, is partly removed; 8, second maxillipede; 9, third maxillipede; 10. forceps; 14, fourth ambulatory leg: 15, first abdominal appendage; xv.. first, and xvi., second abdominal somite; arb.8, arb.9, arb.13, the posterior arthrobranchiæ of the second and third maxillipedes and of the third ambulatory leg; arb.’ 9. arb.’ 13. the anterior arthrobranchiæ of the third maxillipede and of the third ambulatory leg; pbd.8. podobranchiæ of the second maxillipede: pbd.13.. that of the third ambulatory leg; plb.12. plb.13, the two rudimentary pleurobranchiæ; plb.14, the functional pleurobranchiæ; r, rostrum.

English one, which in France lives side by side with it. The smaller crayfish, which alone occurs in England, is known as A. torrentium. This specific title will, it is to be feared, have to be adopted, although it by implication casts a slur upon the river Isis. A. Fluviatilis has red tips to its legs and a rostrum which differs by a notch or two from that of A. torrentium. Further, and this is very curious, A. torrentium never has been found to be infested by that very interesting parasite (more interesting even than the crayfish itself), the crab-

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