116 Mr. C. Spence Bate on the Developinent q/Tagurus. 



they may continue to cast their exuvium and grow, during 

 the whole time that they are deficient of such shell, because 

 I have taken specimens occupants of shells that are still 

 smaller than the one described, and yet further advanced to 

 maturity. It would be curious to see if, were they deprived 

 entirely of the use of a shell for a habitat, they would con- 

 tinue to grow and retain the normal form of the pleon gene- 

 rally — a feature that characterizes some of the exotic closely 

 allied genera. 



Thus a careful examination of numerous specimens has 

 enabled us to demonstrate the progressive development of the 

 genus Pagurus^ and to affirm with much confidence, judging 

 by the descriptions and figures of the authors, that the genera 

 Glaucothoe of M. -Edwards and Prophylax of Latreille are no 

 other than an immature stage of the genus Pagurus ; but since 

 their specimens were exotic, they are probably the young of 

 some foreign species. 



Amongst the macrurous Crustacea we have had the oppor- 

 tunity of examining and figuring the larva of Palinurus (PL X. 

 fig. 2). The young of this genus was first made known to the 

 British Association by the late Mr.E,. Q. Couch, of Penzance, at 

 the Meeting at Dublin, in 1857, when he drew attention to the 

 near resemblance existing between it and the genus Phyllosoma. 

 In 1864-65, M. Grerbe, in the ^ Comptes Rendus,' repeated 

 the discovery of Mr. Couch, and asserts that the larva of Pali- 

 nurus is identical with the genus Phyllosoma, and that conse- 

 quently the genus Phyllosoma is the young of the genus Pali- 

 nurus. 



The larvae of most of the Decapod Crustacea have the largest 

 amount of development commencing with the cephalon and 

 the pleon ; whilst in the larva of Palinurus the greatest ad- 

 vancement exists in the anterior part of the cephalon and in 

 the pereion, whereas the pleon is almost rudimentary. 



On comparing it with the genus Phyllosoma (PI. X. fig. 1), 

 as M. Gerbe has done, there is little that can warrant a sepa- 

 ration of the two in the general structure of the animals, 

 or that might not be accounted for by increased develop- 

 ment of the younger specimens. Yet there are certain points 

 that weigh heavily in the balance of evidence against the 

 larva of Palinurus and Phyllosoma being but different stages 

 of the same animal. 



(1) It is contrary to our experience that so small an amount 

 of progressive development has taken place in an animal 

 that has increased in growth to about thirty times its size. 

 We generally perceive, in the development of Crustacea, that 

 tlie most important changes are those that immediately succeed 



