452 ON API'ENDICULARIA FLABELLUM 



" 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 reproduction of the latter rather confirming my opinion.' 



" It is highly desirable that more information should be gained 

 about this extraordinary respiratory organ, whith, if it exist, will not 

 only be quite siii generis in its class, but in all animated nature. And 

 in a physiological point of view, the development of a vascular net- 

 work, 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. 



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

 is one of the Tunieata. The -whole organization of the creature, its 

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

 v\s\x. 



" In two circumstances, however, it differs widely from Tunieata 

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

 the respiratory, the anus opening on the dorsum ; and secondly that 

 there is a long caudal appendage. 



" As to the first difference, it may be observed, that, in the genus 

 Pelonaia} an undoubted Ascidian, there are indeed two apertures, but 

 there is no separation into respiratory and cloacal chambers. Suppose 

 that in Pelonaia the cloacal aperture ceased to exist, and that the 

 rectum, instead of bending down to the ventral side of the animal, 

 continued in its first direction and opened externally, we should have 

 such an arrangement as exists in Appendieularia. 



" With regard to the second difference, I would remark, that it is 



^ I A\oulcl particularly remark that the statement that there is no separation between the 

 branchial and cloacal chambers in Pelonaia is erroneous. At the time this paper was 

 written I had not examined Pelonaia (whose structure, as I have since found, differs in no 

 essential point from that of an ordinary Cynthia), and I must have misunderstood the verbal 

 information given by my lamented friend Professor E. Forbes. 



