84 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



e, and it finally comes to lie under the ventral surface of the right side 

 of the pharynx, Plate XXXVI, Figs. 3, 4 and 5, /. As shown in these 

 figures, the heart arises as a furrow which is formed by the involution 

 of the dorsal surface of the vesicular pericardium. 



This outline of the history of the larger organs of the chain-salpa 

 will give enough insight into the mode of development of its body to 

 enable the reader to understand the more minute and detailed descrip- 

 tion which follows. 



SECTION 2. The General Characteristics of Aggregated Salpce. 



The way in which the proliferous stolon grows out from the body of 

 the salpa embryo and gradually acquires its complicated organization 

 may be spoken of with perfect propriety as budding; but inasmuch as 

 the stolon itself contains the rudiments of all the important systems of 

 organs, its transformation into a series of aggregated salpae by cell 

 multiplication and by the folding of its various parts, is more like the 

 development of an embryo with germ layers into the body of a compli- 

 cated adult than it is like ordinary budding, and it may perhaps be more 

 proper to speak of it as the strobilization of the stolon. It is of course a 

 process of asexual multiplication, but as the stolon contains the potency 

 of all the following generations of chain-salpae, it stands, as Seeliger has 

 pointed out (11, p. 583), in somewhat the same relation to the chain-salpae 

 as that which a young embryo, with its future structure latent in its 

 germ layers, bears to the perfect adult, since, in each case, the process of 

 development consists in the unfolding of its rudimentary organization. 



As a knowledge of the final result will aid us in tracing the minute 

 details of the process, I shall give a short outline of the most conspicuous 

 features before I describe the process of strobilization. 



The growing stolon lies in a chamber which is hollowed out in the 

 cellulose mantle of the solitary salpa, and as the aggregated salpae are 

 set free they escape through an opening which connects this chamber 

 with the exterior. 



In Salpa pinnata, Plate I, Fig. 6 ; Salpa chamissonis, Plate I, Fig. 7 ; 

 Salpa cylindrica, Plate III, Fig. 7, and in a few other species, the stolon 

 lies underneath the middle line of the ventral surface of the body of the 

 solitary salpa, and it is symmetrically placed, with its free or distal end 

 pointing forward, and with its right and left sides symmetrically placed 

 with reference to the plane of symmetry of the solitary salpa. 



