i 



376 JOHN F. FULTON, JR. 



a red substance (vanessa red), which is later absorbed and 

 transported to the epitheHum, where it is deposited and 

 becomes the pigment of the wings and of the other body-parts. 

 The unabsorbed portion of the red pigment is voided. The 

 investigations of Gortner (1911 and 1912 6) on insect melanins 

 are also of interest, since he has shown that they are sometimes 

 formed from chlorophyllous substances (oxidizable chromogens) 

 acted upon by the plant ferment, tyrosinase. More recently 

 Schmidt (1919) has conducted similar investigations on insect 

 melanins, and his results accord with those of Gortner. 



It appears to the writer that the most significant part of all 

 Poulton's work on insects is the demonstration that chlorophyll 

 resists the digestive enzymes, and passes practically unchanged 

 into the blood-system. Evidence has been cited to prove that 

 this also is the case in the Mollusca and Crustacea, but the 

 evidence is not conclusive (except in the case of carotin). In 

 insects, however, there is undisputable proof, and it is of 

 particular importance, since it shows that the theory that 

 haemoglobin as a derivative of chlorophyll must not be ruled 

 out by the fact that chlorophyll is incapable of passing through 

 the digestive tract. In general, then, the epidermal pigments 

 of Crustacea are derived from food and are carried to their 

 destination by the blood-system. 



6. The Tunicata. 



The strongest evidence in support of the view that the 

 epidermal pigments are deposited by the blood-system is to 

 be derived from a study of the tunicates, where it is possible 

 to predict that there will be found in the blood-stream pigment 

 cells of a colour corresponding to that of the tunic. Moreover 

 one can show that the pigmented corpuscles arise from colour- 

 less cells while they are in the circulation. The tunicate to be 

 first considered is Ascidia atra. 



(a) Ascidia atra. 



This species is distinguished from other tunicates, and in 

 fact from almost all other animals, by the possession of an 



