116 Mr. C. Spence Bate on the Development of Pagurus. 
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 
Glaucothoé 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 (PI. X. 
fig. 2). The young of this genus was first made known to the 
British Association by the late Mr. R.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. Gerbe, 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 larvee 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 (Pl. 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 
the most important changes are those that immediately succeed 
