72(> CROZIER. 



a somewhat careful search for it has been made on the basis of its 

 habits, as revealed by such individuals as have been found, only a 

 small number have been seen. It has therefore been impossible to 

 collect a quantity of the animals for purposes of experimentation, and 

 these notes are, in fact, based upon observations made with only six 

 specimens. 



The first individual of this type obtained was found in the branchial 

 sac of a colorless, transparent ascidian, Ascidia curvata Traustedt, 

 which was, as is usually the case with A. curvata, attached to the 

 under side of a flat stone. The polyclad was of fair size, 17 mm. in 

 length when creeping undisturbed. It was observed frequently to 

 come out of the ascidian, and to creep about the aquarium in which the 

 animals were kept. It was marked as shown in Figure 7, but its body, 

 aside from the black cross-bars, was entirely devoid of coloring matter, 

 its substance being of a velvety opaque white appearance. 



Three other specimens were taken among separate colonies of the 

 orange colored Ectinascidia turbinata Herd. 2 growing on the reefs. 

 These colonies of the tunicate were affixed to the dead upper portions 

 of gorgonian "whips." In one instance the colony was closely united 

 with a mass of Rhodozona picta (Verr.), the test of which is gelatinous, 

 transparent, and colorless. 3 The polyclads obtained from the Ecti- 

 nascidia colonies are well depicted in Figure 2. It will be noted that 

 there is a very fair agreement between the general hue of such an in- 

 dividual and that of the test of its host (Fig. 1). 



The remaining two examples were obtained from the dark purple- 

 black Ascidia atra Les. The one illustrated in Figure 7 came from the 

 interior of a dead test of this species, the other, of a much darker cast, 

 being found in the branchial sac of a healthy individual. 



There is an obvious, striking parallel between the coloration of these 

 animals and that of the tunicates with which they were individually 

 associated. That there is any protective (concealing) value behind 

 this, can, I think, be confidently denied. For, as a matter of fact, 

 the flatworms when in exposed positions are perfectly conspicuous in 

 spite of the agreeing element in their coloration. This was notably 

 the case with the specimen found in the branchial chamber of the trans- 

 parent A. curvata. 



2 There is some reason to believe that this species is different from that 

 recorded under this title by Van Name (1902). 



3 It is a curious fact that in the instances of compound colonies, which are 

 not infrequent, the Ectinascidia is practically always the upper, the Rhodozona 

 the lower, member of the group. 



