SCALPELLUM RUTILUM. 253 



great compound eyes of the larva, could be seen at the end 

 of the pouch, opposite the orifice. The larva?, I conclude, 

 crawl in at the orifice, one side of which is formed, as we 

 have seen, of yielding membrane, and scratch out the dead 

 exuviae of the former occupant : certainly, the males are 

 less firmly attached to their pouches, though some small 

 quantity of cement is excreted, than are other Cirripedes 

 to the objects to which they are attached. The small 

 size of the female, and her valves not being thickly edged 

 with chitine, accounts for the males having pouches spe- 

 cially formed for them, instead of being, as in S. vulgare, 

 laterally imbedded in the chitine-border of the scuta. 

 In hereafter weighing the evidence on the nature of the 

 parasites in Ibla and in Scalpellum, the fact of the valves 

 of the supposed female being here modified for the special 

 purpose of lodging the males, will be seen to be important. 

 If we imagine the male parasites to be extraneous animals, 

 and that by adhering to the sack of the Scalpellum, they 

 injure the corium and thus prevent the growth of the shell 

 over an area exactly corresponding to their own size, 

 and so form for themselves cavities ; yet what can be said 

 regarding the preparatory furrows ? surely these narrow 

 lines cannot have been produced by the pressure of the 

 much broader parasites. Must we not see in the furrows, 

 the first marking out, if such an expression may be used, 

 of the habitation for the male, which has to be specially 

 formed by the independent laws of growth of the female ? 



3. Scalpellum pojtilum. PL VI, fig. 2. 



S. (Foem. an Herm.) valvis 14 subrujis : carina? tecto 



piano, utrinque crista rotunda fa instructo; margine basali 



truncato: lateribus sujperioribiis latitudine duplo longioribus. 



(Fern, or Herm.) Capitulum with 14 reddish valves : 

 carina with the roof flat, bordered on each side by a 

 rounded ridge ; basal margin truncated : upper latera 

 twice as long as broad 



£So. 5 



