42 Traces of Unity in the Appendicular 



for example, the first pair of feet is not unlike the 

 third pair of feet in the prawn, and the third pair is 

 absolutely like the first pair of true feet immediately 

 behind them, but the middle pair is developed so as to 

 form the large " pattes ravisseurs," which stand out from 

 the other feet about as much as the cheliferous feet do 

 from the ordinary feet in the lobster. Here, the office 

 of cheliferous feet is transferred from the first pair of 

 true feet to the second pair of foot-jaws a transference 

 which brings out very conspicuously the foot-nature of 

 the foot-jaws. Here, too, the close relationship between 

 the foot-jaws and the true feet is evident in the way in 

 which the true feet close around the mouth so as to be 

 capable of doing the actual work of the foot-jaws an 

 arrangement to which the squilla mantis and its con- 

 geners are indebted for their name of stomapods. The 

 case is plain enough when looked at in this way. Nay 

 it is plain enough in itself, for the " pattes ravisseurs " 

 are manifestly only magnified forms of the feet behind 

 them, with the metatarsi turning back in the same way 

 upon the tarsi, and with strongly dentated instead of 

 merely ciliated inner margins. Indeed the case is one 

 which prepares the way for that which occurs in the 

 isopods and branchiopods, where the only difference 

 between the foot-jaws and the true feet is that which 

 attaches simply to position. 



4. In the prawn and in other decapods as well, imme- 

 diately in advance of the foot-jaws, are three pairs of 

 organs to which the name of true jaws is given, the first 

 pair being the mandibles, the two hindermost pairs the 

 maxillae. These organs are more rudimentary than the 

 foot-jaws, and in some cases they are so very rudimen- 

 tary as to make it difficult to identify their particular 

 parts, but now and then, in different Crustacea, their 



