Manchester Memoirs, Vol. Iviii. (191 3), No. 1. 7 



In this latter section, the exopodite also seemed to 

 have lost some of its original shape, and was very com- 

 pressed and much thinner, but more compact ; no other 

 change in the internal structure could be made out, and it 

 is possible that the attenuated appearance may be due to 

 the partial collapse or shrinkage of some of the larger 

 blood-vessels. 



It will thus be seen that the effect of sea-water on the 

 gills is a very gradual one and does not lead to any 

 sudden change of shape. 



In the case of the Ligias which were immersed in 

 fresh water, the distortion of the gill took place with con- 

 siderable rapidity, being noticeable in every case after the 

 animal had been submerged for about eight hours. 



On examination of a T.S. of these gills {PL II., 

 Figs. 3. and 4.), it was observed that whilst the exopodite 

 remained unchanged, the endopoditc had become very 

 swollen — the lumen had practically disappeared, whilst 

 the cytoplasm appeared very diffuse. 



It is curious, however, that in this case the distortion 

 of the gill lamella was confined only to one side ; owing 

 to this, the lumen appeared squeezed over to a lateral 

 position, and thus was almost obliterated. 



The general effect would seem to be somewhat 

 similar to what was noticed in the forms submitted to the 

 action of sea-water, but in the latter case the result was 

 obtained in a much shorter time, the effect appeared to 

 be greater, and the distortion was always confined to the 

 inner border of the lamella. There was no evidence of 

 any nuclear change in any gill which was examined ; the 

 altered form would seem to be due solely to the effects of 

 the changed pressure acting upon the gill-surface, and 

 causing more or less of a mechanical disturbance in the 

 cytoplasmic portion of the gill tissue. 



