ON CRABS WHICH CLING. 179 



In case of need, Galathea maj escape by having recourse 

 to the ancestral habit of swimming backwards by flapping the 

 abdomen or tail, which is therefore still fairly strong, though 

 hardly comparable to that of a lobster. Among the Galatheas 

 the development of the swimmerets, as the limbs of the 

 lobster's tail are called, is very variable, showing that they no 

 longer possess the functional importance that was theirs 

 in the swimming ancestor. The female retains the tail- 

 limbs more or less and they are utilised for the attachment of 

 developing ova, so that her tail or abdomen is to a large 

 extent modified from a swimming organ into a brood-protect- 

 ing cover. They are, of course, used in the same way by 

 lobsters. 



Even lurking, swimming and walking do not complete 

 the list of the characteristic attitudes of Galathea. It is 

 often found under the larger stones near low-water mark, and 

 in such places it Avill often cling to the under surface of 

 a heavy boulder. In such a position we can notice its 

 legs spread out like the radii of a circle w^hose centre is the 

 bodj', a circumstance which brings out most strongly the 

 contrast between Galathea and the lobsters. In the latter, the 

 body is essentially a long axi>, consisting of a series of parts 

 one behind the other wdth considerable, yet by no means 

 perfect, co-ordination of action between the members of the 

 series. The imperfection of that co-ordination is very 

 noticeable in the nervous system, in which we find fairly 

 separate ganglia or nerve centres for each pair of limbs, 

 among some lobster-like forms. 



In Galathea we still find a series of separate nerve 

 centres in the abdomen, but the nerves to the walking limbs, 

 the appendages of the breast region, all arise from a large 

 nerve centre which has obviouslv evolved throup^h fu-ion of a 

 series of separate ones. This fusion is the secret of the 

 co-ordination to which reference has been made, and it 

 has undoubtedly been further promoted by the shortening of 

 the body. This shortening is in its turn associated firstly with 

 the habit of lurking in holes, and secondly with the habit 

 of clinging to the under sides of stones, for the clinging 

 power is due to the limbs stretched all around as grapplers 

 thrown out from a central and therefore necessarily short 

 body. 



My observations on the breathing arrangements of 

 Galathea are unfortunately too incomplete to be dealt with 

 at present ; but I have no doubt it will be found here, as among 

 many sand and mud crabs, that the notches and teeth on 



