Manchester Memoirs, Vol. Iviii. (191 3), No. 1. 



I. Changes in the branchial lamellae of Ligia oceanica, 

 after prolonged immersion in fresh and salt water. 



By Miss Dorothy A. Stewart, B.Sc. 



(Covimunicated by Professor Sydney J. Hickson, D.Sc, F.R.S.) 

 (Received and read October 21st, igi^. ) 



The series of experiments described below were 

 carried out during the course of last winter in the 

 Zoological Laboratories of Manchester University, the 

 material used being numerous specimens oi Ligia oceatiica 

 which I was enabled to obtain from Swanage through 

 the kindness of Professor S. J. Hickson, F.R.S. 



The group Isopoda, of the Crustacea, can be roughly 

 divided into species which are (i) exclusively terrestial, 

 such as the woodlice, (2) those which are exclusively 

 fresh-water, such as the Asellidae, and (3) those which are 

 exclusively marine, such as the Idoteidae, etc. Among 

 these forms Ligia occupies a somewhat interesting posi- 

 tion, for although it is invariably found in the neighbour- 

 hood of the sea-shore, it is of amphibious habits, and 

 there is a strong probability that it might, in course of 

 time, if external conditions were altered, become adapted 

 to fresh water or a purely terrestial life. 



Ligia is commonly found around the sea-coast, fre- 

 quenting rock-pools, or, more usually, crawling over the 

 stones some distance above high-water mark. 



It appears to prefer a terrestial rather than an aquatic 

 habitat, but some difference of opinion seems to exist as 

 to the exact position of its natural surroundings. 



Deceinbcr jist, igij. 



