106 LIFE BY THE SEASHORE. 



whole process. In Nereis, though the genital products occur 

 only in the posterior region of the body, this part does not 

 separate off as in the Palolo. 



In N. pelagica the modifications undergone by the mature 

 female are less marked than those in the male. The female 

 Heteronereids are very much larger than in the male, and 

 have fewer of the segments modified. The modification is 

 also less marked. It is not uncommon to find large speci- 

 mens with a few merely of the posterior segments under- 

 going incipient modification. One striking characteristic of 

 both sexes of Heteronereids is the presence of a sensitive 

 rosette on the last segment of the body. Further, in the 

 male the eye increases in size and becomes beautifully 

 coloured, and, as already noticed, the colours in both sexes 

 become brighter. These very interesting changes can be 

 followed very readily on the shore, especially in the 

 North. 



Besides N. pelagica, two other species occur free on the 

 shore in most places, in addition to N. fucata, a handsome 

 species found in shells inhabited by hermit-crabs. The two 

 species are N. dumerilii, a rather small form with very long 

 cirri, which forms a tolerably firm tube, and N. cultrifera, a 

 large form in which the dorsal cirri are short, and the back 

 less well arched than in N. pelagica. Both species occur in 

 situations somewhat similar to those affected by N. pelagica, 

 and will be generally found among gatherings of the latter. 

 The distinguishing features are noted at the end of the 

 chapter. To get N. fucata, on the other hand, one must 

 collect a few large specimens of hermit-crabs, especially 

 those which occur in whelk shells, and are, therefore, nearly 

 full grown. Such specimens are sometimes flung on the 

 beach by storms, and though often dead or moribund, are at 

 times living and active. If still alive, put your specimens 

 in clean water, and after a time you will not improbably be 

 rewarded by seeing the hermit entirely recover his disturbed 

 equanimity, and sit, metaphorically speaking, at his ease on 

 his doorstep placidly twirling his long feelers. You may 

 further see protruded above the hermit's head the long 

 feelers and stout palps of a brick-red Nereis. The worm 

 does not completely quit the shell, but protrudes the ante- 

 rior part of the body, and no doubt shares in any food 



