EUPAGTTRTJS. 541 



at the expense of the extensors. The muscles of the 

 young animal in the early Glaucothoe stage only differ 

 in detail from those of the Crayfish or Lobster. The 

 extensors have a general longitudinal course and are 

 well developed ; the flexors comprise several muscles, 

 the descending, transverse, longitudinalis and loop- 

 enveloping, and pleopodal muscles independent of the 

 flexors are present. 



In the change to the adult crab the transverse 

 muscles lose their fibres and disappear, and only 

 remnants of the descending and lateral longitudinal 

 muscles persist, so that the flexors come to consist of the 

 ventral, longitudinal and the loop-enveloping muscles, 

 the former of which are probably the more important. 

 The pleopodal muscles also degenerate and the extensors 

 are extremely weak. A thin layer of fibres — the 

 integumentary muscles — lines the integument beneath 

 the nerve cord ; they are apparently derived from 

 scattered fibres that lie in the same position during the 

 Glaucothoe stage. The columellar prominence is derived 

 from the ventral flexor muscles of the third segment. The 

 flexors are bulky, and those of the right side are 

 considerably larger than the flexors of the left. 



There is nothing in the muscles of the cephalo-thorax 

 which calls for comment. 



REPRODUCTIVE ORGANS (PI. V). 



With the exception of the orifices of the sexual 

 ducts, there is only one point in which the male 

 E. bernhardus differs in external characters from the 

 female. That difference is to be found in the abdominal 

 appendages, so it is quite impossible to distinguish the 

 sex of a Hermit Crab unless it be extracted from the 



