48 HISTORY OF CRUSTACEA. CHAP. VII. 



Troschel's ' Handb. der Zoologie ') have no ciliated buccal 

 lobes, although such organs are possessed by the very 

 similar Periwinkles (Littorina). 



All the marine forms of this section appear to be sub- 

 ject to a more or less considerable metamorphosis. 

 This appears to be only inconsiderable in the common 

 Lobster, the young of which, according to Van Beneden, 

 are distinguished from the adult animal, by having 

 their feet furnished, like those of Mysis, with a swim- 

 ming branch projecting freely outwards. From a figure 

 given by Couch the appendages of the abdomen and 

 tail also appear to be wanting. 



Far more profound is the difference of the youngest 

 brood from the sexually mature animal in by far the 

 greater majority of the Podophthalma, which quit the 

 egg in the form of Zoea. This young form occurs, so 

 far as our present observations go, in all the Crabs, 

 with the sole exception of the single species investigated 

 by Westwood. I say species, and not genus, for in the 

 same genus, G-ecarcinus, Vaughan Thompson found 

 Zoea-brood, 2 which is also met with in other terrestrial 

 crabs (Ocypoda, Gelasimus, &c.). All the Anomura 



2 Bell (' Brit. Stalk-eyed Crust.' p. xlv.) considers himself justified in 

 " eliminating " Thompson's observation at once, because he could only 

 have examined ovigerous females preserved in alcohol. But any one 

 who had paid so much attention as Thompson to the development of 

 these animals, must have been well able to decide with certainty upon 

 eggs, if not too far from maturity or badly preserved, whether a Zoe'a 

 would be produced from them. Moreover, the mode of life of the Land- 

 Crabs is in favour of Thompson. " Once in the year," says Troschel's 

 ' Handbuch der Zoologie,' " they migrate in great crowds to the sea 

 in order to deposit their eggs, and afterwards return much exhausted 



