AND DEVELOPMENT OF PYROSOMA. 197 



of which foTir ascend on this neck, while the others go to the opposite side. The pos- 

 terior tubercle, wliich is here inferior, though very apparent in certain individuals, is 

 imperceptible in most. There arise from it four opake yellowish or brown vessels, which 

 traverse the lower side of the tunic; they are evidently the four cords of the dorsal 

 groove of the Ascidians*. Along the upper edge, opposite the four cords of the dorsal 

 groove, are seen two wide, short canals, of a yellow or muddy-brown colour, placed 

 parallel, and so closely united that they might be regarded as a single canal, bent like 

 a siphon, and extending from the middle of the branchiae to the oesophagus, where its 

 two extremities end. The interior appears to be cellular t- 



" This organ, which is sometimes emj)ty and transparent, seems to me to be analogous 

 to that which M. Cuvier regards as the ovary of the Salpce, or at least as their oviduct ; 

 perhaps it is, at the same time, oviduct and fecundating organ. 



" The ovaries % are orbicular or pyriform, symmetrically opposed to one another, and 

 placed on the sides of the neck of the branchial opening, between the tunic and the bran- 

 chial network, which they usually overlap. They communicate with two small, sometimes 

 coloured ducts, which embrace the neck and descend as far as the loop formed by the 

 siphon-like canals. These ovaries contain a multitude of rounded, very small, but very 

 distinct ova. 



" If I do not deceive myself, the manner in which these germs arrive at maturity is 

 very curious. It would appear that while very small they become detached, one by one, 

 from the ovary, and are successively lodged between the intestine and the bottom of the 

 tunic ; there they continue to grow and to be developed, until their final expulsion. 



" In fact, Ave almost always find in this locality an isolated germ, which varies much in 

 size. "V^'^hile small, it is only a perfectly white and transparent globule, in which a round 

 aperture, like a mouth, is discernible ; when somewhat larger, this hollow globule already 

 exhibits four little reddish spots ; and when larger still, these four spots have become a 

 chain of four small but distinct little foetuses, which encircle the globule for three-fourths 

 of its circumference. Lastly, Avhen it has acquired its full size, the four foetuses, provided 

 with all their organs, are united and form a complete ring. In this state it equals a 

 third of the size of the individual which encloses it. It is, as one sees, a new Fyrosoma 

 already composed of four animals, and will very soon be independent of the large Fyro- 

 soma in which it has originated. How does it escape ? I know not. If, as is j)robable, 

 it makes its exit by the same aperture as the excrements, this opening must be capable 

 of undergoing excessive dilatation. 



" These observations, taken in conjunction with those which I have made upon Botryl- 

 liis, demonstrate that the corj)uscles contained in the ovaries of these animals are com- 

 pound germs, not intended for the growth of systems, but for their multiplication. On 



* The 'anterior tubercle' is the nervous ganglion ; the posterior, merely the anterior end of the endostyle, which is 

 described as the ' cords of the dorsal groove.' 



t This 'organ' is the intestine of Lesueur, and, as I have said above, is nothing but a mass of blood-corpuscles 

 accumulated in the bypopharyngeal sinus. 



X These are not the ovaries, but probablv, as I have already said, renal orgnns. What Saviguy calls their ducts seem 

 to be the lower parts of the peripharyngeal ridges. 



