550 LEPADID.E. 



numerous as almost to touch, and sometimes to run into each 

 other, the included animal being thus rendered distorted. 

 The orifices are directed with respect to the shell indifferently 

 upwards or downwards. From the shape and size of the 

 cavity corresponding to that of the included animal, there can 

 be no doubt, as stated by Mr. Hancock, that Alcippe forms 

 its own cavity. That the action is mechanical I think may 

 safely be inferred from the whole outer membrane being 

 studded with minute, star-headed points of hard chitine, 

 which rise from halo-like little discs of thickened mem- 

 brane, which latter are well adapted to allow the under- 

 lying adherent muscular layer to act on the points, and thus 

 on the surrounding shell. Consequently the points gene- 

 rally show signs of severe attrition, but they are periodically 

 and often replaced, at each exuviation, by new and much 

 sharper points. There are no points on the permanently 

 attached layers of the horny disc, but it particularly deserves 

 attention, that the renewable membrane always extends 

 beyond the circumference of the disc, and is there most 

 thickly studded with the points. We have met, in Litho- 

 trya, with a precisely analogous fact in the extension of the 

 periodically moulted membrane of the peduncle, furnished 

 with star-headed points of chitine, and in addition with 

 minute calcareous beads (which, however, seem soon worn 

 away), beyond the calcareous discs, by which this cirripede is 

 attached in its cavity. We need not feel much surprise at 

 points of chitine being hard enough to wear away shell, when 

 we consider what work the jaws of insects, likewise formed 

 of chitine, will effect. 



With respect to the first commencement of the excava- 

 tion, the pupa, owing to the position of its prehensile 

 antennas, fixes itself with its posterior end almost vertically 

 upwards ; and the young cirripede, after its metamorphosis, 

 from the greater length of the ventral integuments formed 

 round the eye-apodemes, must be thrown backwards into 

 nearly the position represented in PL 22, fig. 12, b. I have 

 not seen a young female at this early age, but I have traced 

 the development of several males, and have found that the 

 lower end of the peduncle, (i. e. what was the anterior 

 end of the pupa), grows at quite a remarkable rate, so as 



