438 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 45. 



one peculiarity about the graphica vessel is the color. This is due 

 to the coloration of the cells of the blood. These are exceedingly- 

 numerous and the vessels of about the outer half, in thickness, of the 

 test, become greatly congested with these black cells. In one other 

 specimen, a very large one from Bermg Sea, the test vessels present 

 something of the same condition, the congestion behig, however, less 

 general and the color a less pronounced black. What the meaning 

 is of this condition of the blood cells in some individuals is far from 

 clear. It ought to be stated that some of the internal parts of the 

 grapMca specimen are dark, almost black, in places. The hypo- 

 physis may be especially mentioned as an example. One might say 

 that these specimens with so much black blood are melanic variants 

 comparable to the black individuals which appear occasionally in 

 several species of higher animals the normal color of which is some 

 other than black. Or it may be surmised that the condition is one 

 of disease; or there may be some other explanation. The color here 

 appears to be quite a different thhig from that in Ascidia nigra. 

 Black pigment is so rare among tunicates that the question of its 

 nature when it does occur is of considerable interest and would repay 

 an investigator who would take it up. 



The point of internal structure which has stood most in the way 

 of identifying not only the single graphica specimen, but also several 

 belonging to the present collection as relortiformis, is the dorsal 

 lamina. In my original description of grapliica I spoke of this as hav- 

 ing ''suggestions of a few remote processes on the edge" of the 

 ''rather broad membrane"; and in two or three of the specimens now 

 examined our rough notes speak of "a slight serration" of the lamina 

 or "intimations of teeth " on the edge. On reexamining most of these 

 instances I find that "teeth" and "serration" and "processes," with 

 the meaning that these terms usually have when used to describe the 

 condition of the dorsal lamina of ascidians, is hardly applicable here. 

 A mors accurate statement would be that in some instances the dor- 

 sal membrane, or a portion of it, is uneven, or irregularly scalloped. 

 This departure from a strictly "plain-edged" condition is, I think, a 

 purely individual matter. 



A few specimens from several of the lots are small (young ?) for 

 the species, and coated to a considerable extent with sand, a state of 

 things which, though so characteristic for many species of Molgula, 

 is strikingly absent in the larger individuals of retortiformis. Hart- 

 meyer has noted the same thing in the collections of the species 

 examined by him; so it may be safe to conclude that young animals 

 are more apt to be sand covered than older ones. 



The large size of some of the individuals deserves notice. One is 

 10 cm. in its greatest extension, and since all the animals approach 

 the sphere in shape the mass of such an individual is great for an 

 ascidian. Other specimens are only a little smaller. 



