184 ON CRABS WHICH CLING. 



clings, and so convey impressions from any part of the 

 periphery. The feelers seem to be of the kind which are of 

 very little use out of water. The antennules or first pair of 

 feelers have the usual flicking function. 



On the whole, therefore, we see an interesting specialisa- 

 tion to the Clinging Habit as we proceed from (xalathea to 

 Porcellana, and we have noticed by the way how primitive 

 these two types are compared with the ordinary crabs, and 

 wnerein lies the contrast between them and these latter. 

 More observation is needed, especially with regard to the 

 breathing process, and to the degree of mental development 

 attained by the different types, while as usual we have only 

 very inadequate information about food and enemies. With 

 more time it Avould have been possible to deal with the ordinary 

 crabs as well, but I must close with a notice of Garstang's 

 valuable researches on them, demonstrating the value (as 

 sieves) of spines and other minutia3 formerly regarded as use- 

 less, though fundamentally important for discrimination of 

 species. This type of research has the special attraction that 

 it is removing the last shreds of argument against the theory 

 of natural selection, and so, though restricted perhaps Avithin a 

 very small province, is none the less contributing to the general 

 progress of the science of natural history. 



