CHAPTER IV. 

 THE ORIGIN OF THE PROLIFEROUS STOLON. 



My own observations on the origin of the stolon of Salpa are by no 

 means in complete harmony with the accounts which have been pub- 

 lished, but I shall adhere to the plan which I have followed so far, and 

 shall try to describe my own observations briefly and simply, leaving 

 literary comment for a later chapter. 



SECTION 1. Outline Sketch. 



The aggregated salpae are produced from a proliferous stolon, which 

 grows out from the body of the solitary salpa. It makes its appearance 

 while the solitary salpa is an embryo, and as it begins to become con- 

 verted into chain-salpae before this is born, its early stages must of course 

 be studied in the embryo. 



The stolon is a tube which is joined, at its proximal end, to the body 

 of the solitary salpa, while distally it ends blindly. Its structure and its 

 anatomical relations are well shown in the following figures. Plate 

 XXXV shows at a' a longitudinal section of a very young stolon, and 

 its position is intelligible, since the entire figure is a longitudinal section 

 through the body of an embryo. This stolon is shown more magnified 

 in Plate XX, Fig. 7, and a series of transverse sections through another 

 stolon at the same stage is shown in Plate XX, Figs. 1, 2, 3 and 4. Plate 

 XLI, Fig. 3, is an embryo a little older than the one in Plate XXXV, 

 and its stolon is seen at st. In Fig. 4 of the same plate the same stolon 

 is shown more enlarged, and it is shown in longitudinal section in Plate 

 XVI, Fig. 5. 



The stolon, st, of the embryo, in Fig. 5 of Plate XLI, is shown more 

 enlarged in Fig. 6, and a series of transverse sections of the same stolon 

 is shown in Plate XXI, Figs. 1-7. In this series, Fig. 1 is the most 

 proximal section, at the root of the stolon, and Fig. 7 the most distal one, 

 near its tip. A transverse section of an older stolon is shown in Plate 

 XVI, Fig. 4; another, of a still older one, in Plate XLV, Fig. 5, and a 

 section through the root or proximal end of the stolon of a fully grown 

 solitary Salpa pinnata is shown in Plate XXXIV, Fig. 1. 



