PROTtiOLEPAS BIVINCTA. 599 



its apex. The penis consists of a papilla, only T^ths of an 

 inch in length, situated on the extreme point of the 

 abdomen, but rather towards the ventral surface. 



Metamorphosis. — In accordance with the general law of 

 the correlation of parts, it may be inferred, from the descrip- 

 tion and measurements of the pupal antennae immediately to 

 be given, that this abnormal creature was developed within 

 a pupa of the same general structure, and of about the size, 

 as the pupae whence Scalpellum, Alcippe, and many other 

 cirripedes are developed. As the ova are of remarkably 

 small size, indeed I have seen no others quite so small, it is 

 certain that the larvae, as in the case with all other cirri- 

 pedes, excepting Oryptophialus, must undergo several meta- 

 morphoses, and increase much in size, before attaining their 

 pupal condition. 



Attachment. — The animal is attached, as already stated, 

 to the sack of the Alepas by two threads, rising close toge- 

 ther from the medio-dorsal line, near the posterior end of 

 the second segment of the body. These threads are attached 

 likewise close together at their further ends, by the an- 

 tennae, into which they enter. They are flattened and strong, 

 yet quite flexible, with a somewhat sinuous surface : they 

 were, in this specimen, ^ths of an inch in length, and a 

 little above ^ths in diameter : where joined to the thoracic 

 segment they were a little contracted. Their structure in 

 this specimen could be made out (PI. 24, fig. 1) with perfect 

 distinctness. Their transparent outer tunic (e, fig. 1) is 

 —nth of an inch in thickness, and is continuous with that (d) 

 enveloping the whole body, but is abruptly and considerably 

 thicker than this membrane; and hence a very slight collar 

 is formed outside, round the line "of junction of each thread 

 with the body. The delicate corium (c) lining the external 

 membrane of the body runs, at least someway, down these 

 threads. It was likewise indisputably evident that the mem- 

 brane (b), for I separated it by dissection, forming the great 

 ovarian sack, together w T ith the cellular contents of this sack 

 (a), entered and extended down both threads. It should, also, 

 be particularly observed, that the coarsely cellular matter 

 within the ovarian sack, immediately that it entered the tube 

 formed by the membrane of the ovarian sack, suddenly changed 



