MONSTROSITIES 317 



No one Avho gives, this subject any attention can look over 

 Mr. Stebbing's History of Crustacea, and also the specimens in the 

 Natural History Museum, without becoming convinced that many 

 of them must have originated suddenly as monstrosities, brought 

 about by some atomic disturbance, during the development of the 

 embryo, and that subsequently natural selection may have further 

 modified the monstrous parts, the animal having found them 

 useful in the battle of life, or at all events found that they did not 

 seriously interfere with its continued existence. 



Look at that unfortunate Dorippe japonica of Fig. 10 (Stebbing's 

 Crustacea). It descended from ancestors that had eight fully 

 developed walking legs, but Dorippe has only four walking legs, 

 and the other four are ludicrously dwarfed and stuck on its back. 

 In the Natural History Mu.seum there is a specimen ticketed D. 

 dorsipes 1 Then look at the figures on Plate vii. Every one of the 

 specimens has either one pair or two pairs of atrophied legs, just as 

 if you saw an adult Man with a normal body and two little ' wee 

 legs ' at the end of it, like those of a newly born baby. 



Stebbing says: 'To account for their dorsal position various 

 reasons have been suggested. Herbst says the Crab can run 

 either way up.^ Another view is that these hind-legs lift foreign 

 objects on to the carapace, and a third, that they help to repel 

 animals that might otherwise tread on the Crab's back.' 



Whatever may be the use the Crab makes of them now, the 

 dorsal legs are best explained as having originally been brought 

 about as a monstrosity, which the animal had the good sense to 

 make the best use of, if it had to exist at all. 



The curious part of it is that, with all its anomaly and sup- 

 pression of four legs from the function of progression, Dorippe has 



' I suppose, when it gets tired of running one way, it throws itself on its back and 

 runs on the other way, so that it can tire out its enemies ! 



