486 TUNICATA. 



inner tunic of an adult Ascidian. This tubercle becomes elongated by 

 growth into a tube, the extremity of which is closed, but free, while 

 its internal cavity communicates freely by the opposite end with the 

 abdominal cavity of the Ascidian from which it originally sprouted ; so 

 that the blood circulating in the latter easily penetrates into the caacal 

 appendage, wherein an active circulation is kept up. Generally speak- 

 ing, in proportion as these marginal tubes advance into the common 

 tegumentary tissue around them, they divide into several branches, and 

 the extremity of each of them becomes inflated and claviform; soon 

 there appears, towards the summit of each terminal swelling, a small 

 granular mass wherein the forms of an Ascidian gradually develope 

 themselves, and which in time becomes a new animal, resembling those 

 already existing in the common mass, of which it is destined itself to 

 become a new inhabitant. Ultimately the communication between the 

 parent and the young individual becomes obliterated; but still the 

 newly-formed animals, thus derived from the same parent, remain for 

 some time united by their pedicle ; and, apparently, to this circumstance 

 their mode of arranging themselves in groups is due. 



(1276.) The ovary is a whitish glandular mass, imbedded with the 

 liver among the folds of the intestine ; its position in fig. 243 is indi- 

 cated by the letter m ; and at o, fig. 244, it is seen separated from the 

 surrounding structures. The oviduct, which is occasionally very tor- 

 tuous, accompanies the rectum, and terminates near the anal aperture 

 (fig. 243, m, fig. 244,^>) ; so that the ova ultimately escape through the 

 common excretory orifice. 



(1277.) Since the publication of the former editions of this work, 

 important additions have been made to our knowledge relative to the 

 generative system of the class under consideration, and a distinct male 

 apparatus, the existence of which was formerly denied, has been satis- 

 factorily described by many skilful observers. The arrangement of these 

 organs, as they exist in Cynthia ampulla, dissected by Yan Beneden, is 

 shown in the accompanying figure (fig. 246, A, B). In this species the 

 sexual parts appear at first sight to form but a single organ, imbedded 

 in a fold of the alimentary canal (a, 6) ; but by the assistance of a micro- 

 scope, this is readily seen to consist of two portions one male, and the 

 other female. The testicle (c) surrounds the base of the ovary, and is 

 distinguishable by its milky- white colour; its substance is entirely 

 made up of innumerable short convoluted caeca, visible to the naked eye, 

 and resembling the seminiferous tubes of many of the higher animals. 

 Three or four glandular prolongations (/) arise from the surface of this 

 organ, which are hollow internally, and contain a milky fluid which is 

 poured into the cloaca, and which the microscope reveals to be almost 

 entirely composed of spermatozoa with disciform heads and filamen- 

 tary tails. The ovary is of a dark colour, and is imbedded, as it were, in 

 the testes ; its oviduct (e) opens into the cloaca by the side of the anus. 



