284 



KNOWLEDGE. 



[December 1, 1899. 



flow in upon these sheltered branchia3, and may, wlien it 

 has served its turn, by other orifices flow out again. 

 In this business, the second maxillfe are adapted to play 

 a highly important part, supplying a sort of lock-gates 

 or valves, which, in rhythmic beats, regulate the inflow 

 and efflux of the respiratory stream. Here, too, as else- 

 where in nature and art, circumstances alter cases. Thus, 

 Mr. Walter Garstang has shown that the Masked Crab 

 [Cori/stes cassirelaunus), when buried in the sand under 

 water, reverses the usual current. This is almost a neces- 

 sity of its situation. The water-pipe which connects it 

 with its reservoir, the superincumbent ocean, is formed by 

 its long setose antenuip. By utilizing this for the intake 

 instead of as a discharge pipe, the crab obtains good 

 water from above and allows the used-up supply to filter 

 away into the absorbent sand around it. Various crabs 

 have made experiments in the art and mystery of an open- 



and beauty. The explanation is that in the great depths 

 the supply of oxygen is very scanty, and therefore greater 

 and greater sub-division of the branchise becomes desirable 

 for increasing the absorbent surface. 



Very striking also are the branchial organs in the 

 Schizopoda, and these animals are not at all chary of dis- 

 playing them. The sides of the carapace are not jealously 

 folded round but coquettishly raised, as though the crea- 

 ture were saying to itself, " It is a pity you should not see 

 my graceful curls." It is just such a contrast as we 

 find in the harbours of the world, some of which are 

 suspiciously guarded against inspection, while others invite 

 and demand the admiring gaze of every fresh beholder. 



All the Crustacea above mentioned, with one or two 

 peculiar groups to boot, may be said to form a series 

 strictly interconnected in respect to their respiratory 

 system. But important divisions of the Malacostraca 



A'Schizopod, Nemafoxnelis megalopa Sars 



air life. You do not, perhaps, realize the heroism of such 

 an adventure to creatures formed for aquatic respiration. 

 It is something like our sailing in a balloon over Mount 

 Everest. A little economy of resources becomes expedient. 

 To this end some of the little sea-quitting crabs show a 

 pretty adaptation. Instead of having the carapace smooth 

 on its under surface, they have it minutely furrowed and 

 cross-furrowed. Fritz Miiller explained the reason of this 

 ornamentation. The crab, on leaving the water, can take 

 a supply of that element with it in its branchial chamber — 

 a supply, but a strictly limited supply. After expelling 

 this through the 

 efferent orifices at 

 the sides of the 

 mouth, the crab, in 

 the ordinary condi- 

 tion of things, 

 would begin to gasp 

 for want of a breath 

 of water. But the 

 little crabs in ques- 

 tion can let the ex- 

 haling stream 

 trickle through the 

 network of their 

 stomacher, or 

 waistcoat, as one 

 might call it, and 

 it will take up 



oxygen from the outside air and be fit for breathing over 

 again in the branchial chamber. 



It is, perhaps, in the deep-sea prawns that the branchial 

 plumes, as they are called, attain their highest elaboration 



remain, which breathe, not indeed in an entirely different 

 way, but with an entirely different part of the body. 

 Hitherto we have been exclusively concerned with the head 

 and trunk of the animal, leaving the tail to take care of 

 itself. There is sometimes a difficulty in persuading 

 people that a crab has a tail, because the fashion among 

 crabs is to wear it so very thin and small, and to tuck it 

 underneath with a sort of deprecatory air, as if to say, 

 "Oh, no, we never mention it in our family, leastways, 

 not out of the family." In lobsters, on the other hand, 

 and prawns, and a great host of crustaceans which have 



-^^:^ 



Branchise of Nemafoscelis megalops, more highly magnified. From Sars. 



no English names, the tail is muscular and powerful, and 

 might often be called the predominant partner. Still, it 

 does not carry the breathing organs. But when we turn 

 to the rapacious Squillidae, we find a new development. 



