134 JOHNS HOPKINS UNIVEESITY MORPHOLOGIC A.L MONOGRAPHS. 



Pyrosoma, and the more recent accounts by Seeliger (15) and Salensky 

 (17), would, so far as the anatomical structure of the stolon is concerned, 

 serve as a description of the salpa-stolon. In each case the stolon is 

 bilateral in the same plane as the animal which carries it ; in each case it 

 grows out on the ventral middle line near the heart, and in each case it 

 consists of, 1st, an ectodermal tube continuous with the ectoderm of the 

 parent ; 2d, an endodermal tube which arises on the ventral side of the 

 pharynx between the folds of the endostyle ; 3d, two perithoracic tubes, 

 which, in the primary stolon at least of Pyrosoma (Salensky, 17, p. 475), 

 are ectodermal in ultimate origin, as they are in Sal pa; 4th, a nerve 

 tube, or, in the primary stolon of Pyrosoma, a series of nerve vesicles 

 (Salensky, 17, p. 475),which are ectodermal in origin like the nerve tube of 

 Salpa ; 5th, two blood tubes, and, 6th, a genital string. The organs which 

 are derived from these various structures are alike in both cases, and my 

 account of the formation of the aggregated salpaB shows that, morpho- 

 logically, they form a single series placed belly to back, and developing 

 in succession from the tip of the stolon to its base exactly as they do in 

 Pyrosoma, and that each one in the series is joined by its dorsal surface 

 to the ventral surface of the next younger, and by its ventral surface to 

 the dorsal surface of the next older in the series, and that the right and 

 left sides of each one, as well as its dorsal and ventral surfaces, lie, mor- 

 phologically, in the same relation to space as the corresponding parts of 

 the parent. 



In order to appreciate this resemblance in all its details it is neces- 

 sary to master the minute history in each case, but the phenomena are 

 so complicated and their points of agreement so numerous that the 

 deduction seems to be irresistible that the method of asexual multipli- 

 cation has been inherited in both Salpa and Pyrosoma from a common 

 source. 



I believe, therefore, that the present condition of our knowledge 

 enables us to state with confidence that Pyrosoma, Doliolum and Salpa 

 form a natural group, or great branch from the Tunicate stem. 



I have spoken of the various members of this group as closely related, 

 but I have not intended to imply that the relationship is in all cases 

 equally close. Anchinia, Dolchinia and Doliolum are clearly more 

 closely related to each other than to any other Tunicate, and the gen- 

 erally accepted view that, in this group, Anchinia is nearest to Pyrosoma 

 seems to have much to commend it. The various species of Salpa are 

 more closely allied to each other than to any other Tunicate, and Salpa 



