560 MAYNARD M. METCALF, 



of tbe body a mass of germinal cells many of which, though immature, 

 are clearly seen to be ova, while the remaining, smaller cells show 

 no special character. When the stolon is formed from the ventral 

 surface of the body, near this germinal mass, a cord of germinal cells 

 pushes out into the stolon and supplies the developing buds with 

 their reproductive organs. Each bud receives from one to five eggs 

 and a considerable number of the smaller unditïerentiated germinal 

 cells. The latter in part form the follicular envelope for the egg or 

 eggs, and in part form the testes. The eggs, when received by the 

 buds from the parent, are already well along on the road to maturity, 

 while the testes are still wholly undifferentiated. In this group, there- 

 fore, we would least expect to find any exception to the usual rule 

 of protogyny. It is, however, here, in one of the common species, 

 that we find the only case of protandry which, so far as I know, has 

 been found among the Tunicates. 



In the young Salpa cylindrica buds upon a stolon which has a 

 diameter of a little less than one millimeter, we find in each bud a 

 single ovum with its follicle , and a small mass of undifferentiated 

 cells near by, destined to form the testes. In these buds the elaeo- 

 blast, which is to be interpretated as a vestigial tail corresponding 

 to the tail of the Ascidian tadpole, is typically developed, having the 

 characteristic vacuolated or spongy appearance. 



In older buds which have reached a length of nearly one milli- 

 meter, we find the elaeoblast has been replaced by a bilobed mass of 

 cells that has grown down into the posterior end of the bud (Fig. 61 t). 

 Study of intermediate stages shows that the invading mass is derived 

 from the Anlage of the testis, and that, as it pushes into the 

 elaeoblast, it enlarges rapidly, soon so crowding the latter as to cause 

 it to disappear. The ovum has still the same size and character as 

 when first received from the parent form. 



In buds one and one-quarter to one and one-half millimeters in 

 length we find that the testis when sectioned shows, in the lumiua 

 of its tubules, great numbers of adult spermatozoa with fully de- 

 veloped tails. Some of these are attached by their heads to the cells 

 lining the tubules; others are lying free in the lumina. The egg in 

 each bud is still immature. 



It is only in much larger buds, three to five millimeters in length, 

 in which the testes have entirely disappeared that we find mature ova 

 of large size and with the characteristic complete double follicle. 

 The spermatozoa, then, in this species, mature and are discharged 



