390 MR. HANCOCK ON THE ANATOMY OF THE FRESHWATER 
the membranous sheath, ¢ ; at first very short, no more than the 
scalloped margin of the cup-formed disc ; but rapidly lengthen- 
ing, fig. 5 a, they soon advance more than half way up the 
sheath. The polype-retractors, figs. 4 7 & 5 g, by this time are 
considerably developed, and the retractors, k, 2, of the tube are 
distinctly visible ; the tube, fig. 57, now begins to bulge, and 
the inverted margins of the orifice are seen within, united to the 
upper end of the tentacular sheath: the parietal muscles, h, also 
make their appearance at this time, and the stomach, ¢, intestine, 
d, esophagus, b, and tentacles having all assumed their proper 
forms, the young animal is ready for protrusion. The buds of 
Paludicella, however, do not all originate from the extremity of 
the old cell ; some sprout from the side, and then a slight swell- 
ing takes place on the inner surface of the tunic. The horny 
sheath soon afterwards begins to bulge, and an external cell 
being formed with its lining membrane, an oval bud makes its 
appearance, and development goes on as just described. 
Tt has been long known that these animals propagate by eggs 
as well as buds. Raspail appears to have described the anatomy 
of the egg and the hatching of it, and the subsequent growth of 
the young polype has been minutely investigated by Sir J. G. 
Dalyell. But the generative organ remained unrecognized until 
it was pointed out by Professor Allman. The appendage to the 
lower extremity of the stomach, considered by Trembley to be 
muscular, Professor Allman believes to be an ovary: that it is 
so there can be no doubt, as eggs may occasionally be seen in 
connexion with it. Appendages of this kind exist in Alcyonella, 
Plumatella, Fredericella, and Paludicella, and will probably be 
found in all Ascidian polypes. In Plumatella and Fredericella 
there are however three of these appendages or filaments, Pl. IV., 
figs. 4 f, d, d, & 5 «, e’, h, h, which are all attached to the lowest 
part of the stomach, and passing down have their other ends at- 
tached to the wall of the cell, not far from the insertion of the 
polype-retractors. It is difficult to say whether all three are con- 
nected with the generative function, or whether some of them are 
not muscles for the retraction of the stomach. A bundle of such 
retractors has been described by Dr. Farre, in the marine species 
