340 JOHN F. FULTON. JR. 



PART I. THE PIGMENTS OF ANIMALS HAVING 

 NO BLOOD-VASCULAR SYSTEM. 



1. Introduction. 



In the study of marine invertebrates one of the most impres- 

 sive things encountered is the great richness and variety of 

 colour ; it is not surprising, therefore, that the question of 

 animal coloration has long engaged great attention. Investi- 

 gated at hrst superficially by those who sought an explanation 

 of the so-called phenomenon of ' protective coloration ', the 

 problem attracted, during the latter part of the nineteenth 

 century, the attention of several English physiologists, and it 

 is to the investigators of this group — Lankester, ^Sorby, Mac- 

 Munn, Mosley, Griffiths, Poulton, and Halliburton are the more 

 important names — that we are indebted for very real contribu- 

 tions to our knowledge of animal pigments ; especially for the 

 introduction of the microspectroscope into this field of biological 

 research. Since 1900 the work on pigmentation has been to 

 a very large extent spasmodic, and while certain valuable 

 additions have been made (in particular, those of Gamble and 

 Keeble) there are still many problems which invite further 

 investigation. 



The present paper aims to show that the pigment which 

 is responsil^le for the colour of certain representative inverte- 

 brates comes from the blood-stream, and that in many cases 

 the pigment cells of the blood arise (while in circulation) from 

 unpigmented corpuscles. This view concerning the origin of 

 pigment occurred to the writer after noting that a pigment of the 

 blood appeared to be identical with the body pigment in three 

 representative phyla : (1) in another paper the Avriter (Fulton, 

 1921 h) has shown that the pigmented corpuscles in the blood 

 of a Bermuda tunicate, Ascidia atra, arise in the blood 

 from colourless cells, and that the blue pigment cell, so common 

 in the l^lood-stream, is identical with the blue cells of the 

 tunic — the cells which give to this ascidian its intense blue 

 colour ; (2) Crozier (1916 h) has demonstrated that the blue 



