REMARKS UPON APPENDICULARIA AND DOLIOLUM 73, 



development of a lamina from the " semicylindrical organ " (gang- 

 lion ?). This, as it grows, protrudes through the opening at the apex 

 of the animal (respiratory aperture). Its corners then become bent 

 backwards and inwards, and thus a sort of horn is formed on each 

 side, the small end of which is turned towards the apex of the animal, 

 while its mouth looks backwards, downwards and outwards. 



At the same time two other horns are developed upwards (the 

 animal is supposed to have its small end downwards), one on each 

 side. These are smaller and more convoluted than the others. 



This four-horned structure consists of a very regular network of 

 vessels, in which, at the time of the development of the organ, a very 

 evident circulation is visible ; the blood-corpuscles streaming from the 

 attached end of the organ. " The clearness with which the circulation 

 was perceptible, together with the great abundance of vessels and the 

 large extent over which they were spread, were circumstances which 

 led me (says Mertens) to believe this truly enigmatical structure to be 

 an organ, whose function was the decarbonization of the blood. The 

 ease with which the animal becomes separated from this organ is no 

 objection to this view ; the necessity there seems to exist for the re- 

 production of the latter rather confirming my opinion." 



It is highly desirable that more information should be gained about 

 this extraordinary respiratory organ, which, if it exist, will not only be 

 quite sui generis in its class, but in all animated nature. And in a 

 physiological point of view, the development of a vascular network, 

 many times larger than the animal from which it proceeds, in the 

 course of half an hour, will be a fact equally unique and startling. 



86. As to the zoological relations of Appendicularia, its discoverer, 

 as we have seen, considers that " it may possibly be allied to Cesium," 

 a conjecture in which no one can possibly coincide. 



Mertens, on the other hand, says, " The relation of this animal with 

 the Pteropoda is unmistakeable ; if the Oikopleura possessed two tail- 

 like appendages, every one would recognize in them the wings of the 

 Pteropoda ; " and he proceeds to draw, what seems to me, a very forced 

 comparison between Oikopleura and Clio. 



I do not think that any one who has read the preceding pages will 

 be at all disposed to agree with Mertens either. 



87. For my own part, I think there can be no doubt that the animal 

 is one of the Tunicata. The whole organization of the creature, its 

 wide respiratory sac, its nervous system, its endostyle, all lead to 

 this view. 



In two circumstances, however, it differs widely from all Tunicata 

 hitherto known. The first of them is, that there is only one aperture. 



