86 JOHNS HOPKINS UNIVEESITY MORPHOLOGICAL MONOGRAPHS. 



surfaces of all turned towards the root of the stolon, with all their right 

 sides on the right of its plane of symmetry and their left sides on its left, 

 and with their long axes at right angles to the long axis of the stolon, 

 and their oral ends above, as they are shown in the diagram, cut M. 

 As they increase in size, however, and become crowded, they push out of 

 the line to the right and left alternately, and thus form two ranks instead 

 of one. At the same time the body of each salpa rotates ninety degrees 

 upon its own axis, so that the neural or dorsal surfaces come to face out- 

 wards, while the left sides of those on the right and the right sides of 

 those on the left become turned towards the base of the stolon, and the 

 planes of symmetry of the salpae, instead of coinciding with the plane of 

 symmetry of the stolon, make right angles with it. It is most important 

 to grasp clearly the fact that this position is a secondary one, and that, 

 morphologically, there is only a single series of animals, all placed in the 

 same position and all facing the same way like a single file of soldiers ; 

 for the change of position takes place at a very early stage, and all the 

 published accounts of the budding of salpa are so vitiated by a failure to 

 discover it, or else to understand it, that they are almost worthless. 



The chain-salpae of Salpa scutigefa, Plate IV, Fig. 1, retain this 

 secondary position after they are born, but in most species this arrange- 

 ment, which persists in Salpa scutigera, is transitory, and still other 

 changes of position soon take place. 



The position which is shown in cut M may be called position one, and 

 the position which persists in Salpa scutigera, position two. In every 

 species the salpse arise in the stolon in position one, which may therefore 

 be called the true, or morphological, position, and in every species they 

 quickly assume position two. Plate VIII, Fig. 1, shows two of the aggre- 

 gated salpae of Salpa pinnata in this position, and Fig. 2 two of Salpa 

 cylindrica. 



This position is also shown in sections of Salpa pinnata in Plates 

 XXXVI, XXXVII and XXXVIII, and in sections of Salpa cylindrica in 

 Plates XXXIX and XL. These plates, and Plate XV and Plates XXIII 

 to XXXIII, represent sections which are parallel to the long axis of the 

 stolon, and transverse to the bodies of the salpae, and in all of them the 

 right side of the stolon is on the right side of the figure, and its proximal 

 end towards the bottom of the page. 



In Salpa pinnata, Plate I, Fig. 2, and Salpa chamissonis, Plate XLI, 

 Fig. 9, only a few aggregated salpse, about eight in Salpa pinnata and 

 twelve in Salpa chamissonis, are set free at one time, and these, just 

 before they escape, arrange themselves in a wheel or rosette with their 



