INTRODUCTION. Iv 



If this figure be correct, we have a remarkable approach 

 in the general form of this species to that of some of the 

 smaller Macroura, as observed by Mr. Thompson and 

 Capt. Du Cane; but the details scarcely agree with the 

 full and doubtless correct description of the former author. 

 The researches of Mr. Rathke * are, in fact, of great 

 value, as affording the only clue we have yet seen, to 

 the homologies of the members which exist in this early 

 condition of the animal. It appears from this account, 

 that the true feet are not represented by the three pairs 

 of locomotive organs which are observed in the early 

 stage, but that these are in fact developed into the foot- 

 jaws of the adult. " Embryos about to escape have only 

 three pairs of members that can serve for locomotion. 

 All these six members are not, as might be expected, 

 true feet in a lower state of development, but the foot- 

 jaws. Of true legs, and also of branchiae, there does 

 not yet exist a trace." It is not until a subsequent period 

 that these organs are formed, and, in fact, the whole 

 account of the development of the young Paguri, as 

 given by M. Rathke, is highly interesting, and would 

 be particularly useful as a guide to those observers who 

 might have the opportunity of watching the whole pro- 

 gress of any of these animals from the egg to maturity. 

 The most remarkable form of the larva amongst the 

 Anomoura hitherto observed, and, indeed, one of the 

 most anomalous in the whole Decapod group, is that of 

 Porcellana plafycheles, as described and figured by Mr. 

 R. Couch, in his second Memoir. There is no appear- 

 ance of either dorsal or frontal spines, in which respect 

 it agrees with the Macroura, as it does also in the com- 



* Ann. of Nat. Hist. vol. vi. p. 2C3. 



