W. K. BROOKS ON THE GENUS SALPA. 227 



relative numbers of ovarian and mature eggs, and the facts seem to me 

 to warrant the directly opposite view, that the number of cells in the 

 embryonic germinal mass is very much smaller than the total number 

 of eggs which each solitary salpa produces. Even in the oldest stolon 

 the germinal cells at the base are in active multiplication, and new 

 ovarian ova are continually arising at its root and traveling outwards 

 to take the places of those which have been carried away in the bodies of 

 successive broods of chain-salpae. We know nothing regarding the birth- 

 rate of salpa, except that it must be very high, for in calm weather it 

 multiplies so rapidly that the surface of the ocean quickly becomes 

 crowded by innumerable multitudes, and when kept in captivity in an 

 aquarium the solitary form of Salpa democratica discharges chain after 

 chain without any evidence of exhaustion. I know of no observations 

 upon the maxinjum birth-rate of any species of salpa, but the great 

 number of buds upon the stolon is an indication that it is very great 

 indeed. Salpa democratica usually has three or four sets of buds upon 

 its stolon at one time, and Leuckart (p. 67) found forty in one set and 

 sixty-five in another. Seeliger figures thirty-one in the same species on 

 one side of a set, or sixty-two in all, and sixty is probably very near the 

 average for the species, and multiplying this by four we get from two 

 hundred to two hundred and fifty as the number of segments of the 

 stolon. 



I find that a single set of buds from the stolon of Salpa cylindrica 

 contains about two hundred, so that the whole number in the stolon at 

 one time in this species is six or eight hundred, and the stolon of Salpa 

 pinnata usually has from two hundred to two hundred and fifty buds. 



Salpa democratica gives birth to a great many chains, and our 

 scanty knowledge indicates, so far as it goes, that the number of buds 

 which are found in the stolon at one time is only a very small part of the 

 total number which each solitary salpa can produce, for the process of 

 the formation of new buds is continually going on even in the oldest 

 stolon, and there is always a reserve of ova at the base, and I have never 

 seen anything to indicate that the process of budding ever comes to an 

 end through the loss of the power to bud or the exhaustion of the supply 

 of eggs. In some species, such as Salpa hexagona, each bud contains five 

 eggs, and we may safely assume that the germinal mass represents in 

 itself the possibility of many thousand eggs. 



I have tried to estimate the number of nuclei in the germinal mass 

 at the stage which is shown in Plate XX, Fig. 6, and in Plate XLI, Fig. 7. 



