21 



liuiii of the blond vossols, and probably also the onveb)])- 

 iiig iiieiubrane of the g-onads. Tlie inteicelliilar substauco 

 formed by these cells is struetuieless and of g-elatinons 

 appearance, and takes a deep colour with many staining- 

 reagents (especially hannatoxylin or nigrosin). 



(2) Pigmented connective tissue without intercellular 

 substance. This occurs in the cutis, and consists of 

 meuLbraneless cells Avith tiue branching fibrils containing 

 greenish yellow [)igment granules. It is more plentiful 

 on the dorsal surface where the colour is darkest. 'J'h(» 

 amount and distribution of this pig'ment 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 

 up(ui as due to the refraction of light rays coming from 

 the greenish pigment. 



(3) Mesenchyme tis.sue composed of bi- or multi-polar 

 cells without intercellular substance. This tissue is much 

 reduced in the present sjjecies, being only found in the 

 anteiior region of the l)ody between the proboscis sheath 

 and the (esophagus. 



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

 lated cells with an outer membrane. 'I'his occurs round 

 the dorsal and lateral blood vessels in the intestinal 

 it'gicm (PL I\'., fig. '-vM, though it is not pi-esent on the 

 conimissurul vessels. 



BODY C.WITV .\XD ca).\Al)S. 



While some t)bservers hold that no body cavity is 

 present in the Xemerteans, otheis consider that it is repre- 

 sented 1)y spaces sometimes found lound the alimentary 

 canal, and in which occur mesenchyme cells. Such spaces 

 ai'c in some species w(dl marked with the mesenchyme 

 cells so arranged as to foiia a more or less (lefinitc lining 



