262 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Hum of the blood vessels, and probably also the envelop- 

 ing membrane of the gonads. The intercellular substance 

 formed by these cells is structureless and of gelatinous 

 appearance, and takes a deep colour with many staining 

 reagents (especially hematoxylin or nigrosin). 



(2) Pigmented connective tissue without intercellular 

 substance. This occurs in the cutis, and consists of 

 membraneless cells with fine branching fibrils containing 

 greenish yellow pigment granules. It is more plentiful 

 on the dorsal surface where the colour is darkest. The 

 amount and distribution of this pigment probably deter- 

 mines the colour variety (i.e., whether red or green), 

 since a greater amount of pigment usually occurs in the 

 red variety. On this view the red colour must be looked 

 upon as due to the refraction of light rays coming from 

 the greenish pigment. 



(3) Mesenchyme tissue composed of bi- or multi-polar 

 cells without intercellular substance. This tissue is much 

 reduced in the present species, being only found in the 

 anterior region of the body between the proboscis sheath 

 and the oesophagus. 



(4) Parenchyme tissue consisting of large, much- vacuo- 

 lated cells with an outer membrane. This occurs round 

 the dorsal and lateral blood vessels in the intestinal 

 region (PL IV., fig. 2), though it is not present on the 

 commissural vessels. 



BODY CAVITY AND GONADS. 



While some observers hold that no body cavity is 

 present in the jN'emerteans, others consider that it is repre- 

 sented by spaces sometimes found round the alimentary 

 canal, and in which occur mesenchyme cells. Such spaces 

 are in some species well marked with the mesenchyme 

 cells so arranged as to form a more or less definite lining 



