THE CIRRIPEDS. DEGENERATION. 



413 



In the more degenerate cirripeds, the sexes are separate, and the males are 

 reduced to minute forms parasitic on the females. (Figs. 278-281.) 



Degeneration. The wide range of variation in the cirripeds is largely 

 due to the varying amount of degeneration following the metamorphosis. The 

 mantle, integument, and sexual organs are often the only parts that retain the 

 normal powers of growth. The degeneration may be manifest in the dimin- 

 ished size of the whole body, and by the absence, or dwindling of appendages, 

 muscles, alimentary canal, sense organs, and nervous system. The anal opening 



FIG. 281. 



FIG. 280. A, Alcippe lampas, female; about 8 mm. long; B, male, parasitic on disc of female; about r mm. 

 long. Probable position of the remnants of the mouth, indicated at m; cement glands and alimentary canal, 

 absent; excretory organs closed (?). (After Berndt, slightly modified.") 



FIG. 281. C, Scalpellum vulgare, dwarf male; surface view; D, in optical section. Fixed to the hermaph- 

 roditic individuals; mouth and ailmentary canal absent. (After Scott, slightly modified.) 



may close (Petrarca, Fig. 277, females of Alcippe, Fig. 280), or the proctodaeum, 

 stomodaeum, and the entire mesenteron may disappear, as in the dwarf males 

 of Scalpellum (Fig. 281), of Alcippe (Fig. 280), and many copepods (Figs. 282 

 and 283). 



It is doubtful whether these dwarf males survive long after the maturation 

 of the spermatozoa, but there is a certain vegetative vigor in the surviving organs 

 of the larger individuals, i.e., females and hermaphrodites, that is not so seri- 

 ously affected by degeneration. 



The Old Mouth and the New. A highly significant aspect of degeneration 

 in cirripeds is the closing of the mouth (neurostoma), and the dwindling or dis- 



