HERMIT CRAB AND PELTOGASTER. 605 



We will now go on to consider more specially the effect on 

 the sexual characters. 



III. Effect on the Sexual Characters. 



A. The Secondary Sexual Characters. 



The external characters by which the sexes may be distin- 

 guished in E. meticulosus are the following : 



(a) The Cenital Apertures. — In the female these are 

 situated on the internal corner of the basal joint of the third 

 pair of walking legs, and are noticeable oval apertures. 



In the male, on the basal joint of the fifth thoracic leg, there 

 is a papilla directed somewhat posteriorly bearing the male 

 aperture on its apex, bordered with setaceous hairs. 



(b) The Abdominal Appendages. — In both male and 

 female there are appendages present on segments 2, S, 4, 5, 

 6, a character which distinguishes this species from E. bern- 

 hardus, Ion gi car pus, and others in which the appendage 

 of segment 2 is absent in the male, and from E. prideauxi, 

 in which the appendages of segments 2, 3, 4, 5 are all absent in 

 the male. Those of the last segment are paired and form with 

 the uropod the organ by which the crab maintains its hold 

 on the columella of the shell it inhabits. The fifth segment 

 is also furnished similarly in both sexes, bearing a single 

 appendage consisting of a basal joint and two rami, of which 

 the external member is long, and flattened and furnished with 

 an edging of stiff hairs; the internal is pointed and rudi- 

 mentary. The remaining three segments also bear a single 

 appendage, but while in the female these are of markedly bi- 

 ramous character (pi. 33, fig. 6), in the male they are practic- 

 ally uniramous (pi. 33, fig. 1), and similar to that of the 5th 

 segment. 



The relative development of the rami varies slightly in the 

 female. In the second segment the external ramus is but 

 slightly the larger, while in the third and fourth respectively 

 the development of the internal ramus is progressively less. 



