418 
F. A. POTTS. 
itself are so far developed as in Johnson’s form. The latter, 
instead of possessing caudal cirri, ends perfectly bluntly, so 
that apparently tlie number of segments is not yet quite 
complete, and those formed are much narrower than those of 
the stock. It thus appears much more clearly than in John- 
son’s specimen that this appendage is of recent growth. It 
is right, I think, to regard proliferation of stolons as always 
taking place terminally, the reg'eneration of an apjjeudage to 
the stock being a contemporaneous phenomenon. In both 
cases the determining cause of formation is the onset of 
sexual maturity, for gonads are developed in each segment 
of the newly formed extremity of the stock as well as in 
the stolons. A particularly interesting development of the 
phenomenon is exhibited in IX, where the dorsalmost stolon 
(PI. 23, fig. 6) was detached soon after preservation. It was 
3'5 mm. in length, contained thirty-four segments, and had a 
distinctly developed head, with eyes. Evidence of the exist- 
ence of an alimentary canal appeared in a black swelling in 
the middle line of the stolon, and the existence of an opening, 
apparently the anus, just ventral to the caudal cirri. On 
cutting a series of transverse sections the gut was seen to be 
complete from mouth to anus, and functional, as witnessed by 
contained food masses, largely consisting of sponge spicules. 
There can be no doubt that this stolon, the only one of the 
large number developed which possessed the least vestige of 
an alimentary canal, is to be homologised with the genital 
appendage of the stock as observed by Johnson and myself. 
It may even be suggested that this structure normally de- 
velops a head, and becomes detached as a stolon at a late 
period of development, but it is at least equally likely to be 
an individual variation in this particular case. But I think it 
is fair to regard this terminal stolon or appendage as a sur- 
vival from a time when the ancestor of Try panosy llis 
geminipara reproduced by jneans of a single terminal 
stolon, especially if detachment proves to take place usually. 
