REPORT ON THE ISOPODA. 29 



as in the males, but the terminal claw is not yet reflected back. A single male specimen 

 of this species was dredged at Station 164a, which presents some interesting peculiarities 

 in this respect; although only 15 '5 mm. in length, it has all the secondary sexual 

 characters of an adult male ; the epimera are long and project outwards, the anterior 

 ones nearly at right angles to- the longitudinal axis of the body, and the tbird thoracic 

 appendages are fully developed into prehensile organs ; the three middle joints of these 

 appendages, however, are not provided with the soft sensory hairs which I have noticed 

 in nearly all the specimens from Station 168 ; the large male specimen from Station 156 

 is also characterised by the same absence of sensory hairs upon this appendage, and it 

 appears to me to be just possible that the males of this species are dimorphic, one set 

 being characterised by the possession of tufts of sensory filaments upon the third thoracic 

 appendages, and the other set differing by the absence of those structures, and also by the 

 fact that the individuals acquire their own proper secondary characters at an earlier date. 

 It is also possible, of course, that this character may be a mere local variation, but in 

 this case its occurrence in individuals from two such widely separated localities as 

 Stations 164a and 156 is not a little remarkable, especially when we consider that the 

 depths which the species inhabit are so different (400 and 1975 fathoms) in these two 

 localities. 



The time at which the females" of Serolis attain to sexual maturity corresponds in 

 every case to that observed in the case of the males. 



In Serolis cornuta only the largest female examples had the ovigerous lamella3 fully 

 developed, though rudiments of these structures are apparent in many of the smaller 

 individuals. 



In Serolis schythei, corresponding to the early sexual development of the male, the 

 ChaUeuger collection contains a female specimen only 13 mm. in length, but having 

 the brood lamellae fully developed and containing eggs. 



Oi Serolis hromleyana there is an adult female dredged at Station 168, only 22 mm. 

 in length ; in this species, as already stated, the males acquire their secondary sexual 

 characters at a corresponding age. 



