42 SUMMARY OF CURRENT RESEARCHES RELATING TO 



S. Crustacea. 



Adaptations of Limbs in Atyoida Potimirim* — This Brazilian 

 fresh-water shrimp to which Dr. Fritz MuUer has already f drawn 

 attention in counection with its coloration, is now described on 

 account of the peculiar structure of its first thoracic leg and some 

 other of its appendages. Instead of being constructed, as in the 

 immediate allies of Atyoida, | to cleanse the branchial cavity, the 

 appendage mentioned acts as a kind of spoon to provide the mouth 

 with supplies of the fine mud on which this species lives. "Whereas 

 in the nearly allied genus Palcemon, the " hand" (propodite) is long, 

 and provided with a grasping apparatus in the form of a long slender 

 thumb and movable finger (dactylopodite), in Atyoida, the proximal 

 portion of the hand is almost aborted, the finger being articulated to 

 the thumb itself almost in the joint between the hand and carpopodite. 

 The end of each of these parts is provided with a tuft of long bristles, 

 which, when the hand is open, form a kind of fan which detains the 

 fine mud ; when the hand is closed the bristles are closed around the 

 mud, compressing it into a pellet, which is passed into the mouth 

 with great rapidity ; the same takes place with the three following 

 maxillipedes. Further, the posterior maxillae, the first and the 

 middle maxillipedes, have each an unusually long and straight inner 

 edge, fringed with bristles of peculiar form, and, in conjunction, 

 forming an organ admirably adapted for receiving the pellets of mud 

 brought in by the legs. The mandibles form a remarkable exception 

 to the rule in the order, in being unsymmetrically developed, a con- . 

 dition which appears to be rather due to preservation of an ancestral 

 character than acquired by adaptation, as the jaws in their earlier 

 stages resemble those of the Cumacea and Amphipoda. 



The 3rd, 4th, and 5th maxillipedes bear the usual appliances for 

 grasping water-plants; but the lower edge of the dactylopodite of 

 the 6th pair is provided with a comb-like appendage for cleansing the 

 abdomen ; for this purpose the abdominal appendages are successively 

 bent forward and subjected to its operation, and finally the tail itself. 

 The branchial chamber is cleaned by the 2nd pair of maxillae, the 

 outer part of which is usually known as the scaphognathite ; its 

 epipodite portion, instead of being short and broad, is long and 

 narrow, tapers to a point, and carries a dozen long flexible bristles, 

 and is thus able to reach as far into the chamber as the gill of the 3rd 

 ambulatory leg, and to reach with its bristles to the very extremity 

 of the chamber, and thus to traverse all the surface of the branchiae. 



Another contrivance serving the same purpose, is the set of small 

 sausage-shaped processes which spring from near the anterior edges 

 of the coxopodites of the posterior maxillipedes, and the three 

 anterior ambulatory legs ; each process carries about a dozen long 

 hairs and lies back over the coxopodites, and being placed in the 

 entrance to the gill-chamber, hinders, in conjunction with its fellows, 

 the admission of foreign objects. The want of a similar provision in 



* Kosmos, viii. (1881) pp. 117-24 (20 woodcuts), 

 t Of. this Journal, i. (1881) p. 452. 

 J See this Journal, ill. (1880) p. 63. 



