ANIMAL CHLOROPHYLL 361 



pigmentation of nemerteans ; one form. Polia sangiii- 

 r 11 bra, however, is distinguished by the presence of haemo- 

 goblin in the blood-cells (Hubrecht, 1874). Previously 

 Lankester (1872) had found haemoglobin dissolved in the 

 plasma of this form. In'Cerebratulus urticans (Hubrecht 

 and 8hipley, 1911) haemoglobin is found in the wandering 

 body-fluid cells. It is reasonably certain, therefore, that the 

 red colour of certain nemerteans is due to the presence of 

 haemoglobin in the blood and in the body-fluids. The origin 

 of the haemoglobin is not known, but it is interesting to 

 note that the food of these worms is largely chlorophyllous. 



3. MOLLUSCA. 



Among the molluscs the most highly-coloured groups are 

 the opisthobranchs and the cephalopods, and to these brief 

 consideration will be given. 



(a) The Opisthobranchs. 



Crozier (1914, 1916 a, and 1916 d) found that the coloured 

 substance in the mantle of the nudibranch Chromodoris 

 zebra is very sensitive to the presence of acids and alkalis, 

 being blue in its natural state (alkaline) and pink in acid. He 

 (1916 h) observed further that the blood-cells contain a pigment 

 which is similar in colour to the mantle pigment and likewise 

 turns pink in the presence of acid. An examination of the 

 absorption spectra of the two coloured substances showed that 

 they are identical. Thus the pigment of the blood is the 

 same as the pigment which is responsible for the external 

 coloration.^ Inasmuch as it has been shown that the pigment 

 cells in the blood of other forms — echinoderms (Part I of this 

 paper, p. 357) and Tunicates (Fulton, 1921 6)— arise while in 

 circulation, it is not unreasonable to assume, until further 

 evidence is afforded, that the blood-pigment of C. zebra 

 is also synthesized by the moving blood. 



^ The writer attempted to secure specimens of C . z e b r a when inBernmda 

 in order to find the origin of the pigment cells of the blood, but owing to 

 the scarcity of this species during the summer months none were obtained. 



C C 2 



