COMPLEMENTAL MALE. 239 



the increase is also less than is usual, namely, from ^ths 

 of an inch, the diameter of the ovum, to only y—ths of 

 an inch, the length of the boat-shaped larva, just before 

 its final metamorphosis. 



Habits and Concluding BemarJcs. — The males are im- 

 bedded in the spinose chitine border of the occludent 

 margin of the scuta, exactly over an oblique fold or 

 notch (Hg. 15 a a), close by the umbo. This fold has no 

 direct relation to the males, but being present is taken 

 advantage of by them ; for it occurs in the young her- 

 maphrodite, before the attachment of the males, and in 

 species of the genus in which the males are attached 

 to other parts. It occurs, also, in fossil species of 

 Pollicipes, and in these it seems caused by the upper 

 inner part of the valve being rendered more and more 

 prominent during growth : in the present species, I sus- 

 pect, its origin is connected with the formation of a 

 ridge bounding the outer side of the pit for the adductor 

 scutorum muscle : we shall see in the next species, that 

 this fold is of the highest importance in relation to the 

 position of the Males. The transparent chitine border 

 of the scuta is broad, and fills up the fold in the shell, so 

 that the outline of the occludent margin is not affected 

 by it : in the drawing (fig. 9) some of the inner layers of 

 chitine (e e), which dipped into and filled up the fold, 

 have been removed, that the lower part of the animal 

 might be more plainly exhibited. The chitine bears 

 numerous spines of various lengths, which must afford 

 some protection to the males, rudely arranged in lines, 

 parallel to the edge of the valve, indicating the successively- 

 formed layers of chitine ; each spine has a fine, tortuous 

 tubulus connecting its base with the under-lying corium. 

 The extreme outer edge of the border is thin, forming a 

 kind of lip, close beneath which the delicate tunic lining 

 the sack is attached. During continued growth, the 

 valve is added to in thickness, and so is the chitine 

 border, and likewise in breadth. It appears that the 

 larva of the male must attach itself on the under side 



