304 BULLETIN OF THE 



seem to be the first traces of the " tubular hepatic system " ; a layer 

 of anastimosing tubes which, in the adult, covers the outer surface of 

 the stomach and intestine, and opens into the stomach at its anterior 

 end. The function of this organ is much disputed, but as nothing 

 definite is known upon the subject, a history of the discussion is not 

 necessary here.* 



The Testis. — In the adult Chain-salpa, the digestive organs are cov- 

 ered, outside the " hepatic organ," by the glandular organ shown in 

 Fig. 5. This is a layer of arborescent folicles opening into the atrium 

 by two apertures (1), one on each side of the anus (2) ; and a micro- 

 scopic examination shows that it is the testis. It is found only in the 

 Chain-salpa, which is therefore a male ; while the ovary is developed 

 within the body of the solitary Salpa, and will be described at length 

 in connection with the development of the chain. 



Fig. 6. 



Spermatozoa, from the testis of an adult and from the branchial sac of an immature male. 



The Ganglion and Sense Organs. — As an adaptation to its loco- 

 motive life, the nervous system of Salpa is more highly developed 

 than in most of the adult Tunicata, and is provided with highly spe- 

 cialized sense-organs, which are supposed to be those of sight and 

 hearing. The structure of these organs is described at length in the 

 papers by Vogt, Leuckart, and H. Miiller already referred to. 



The Heart and the Circulation. — Since the discovery by Van Hasselt 

 in 1824, that the circulation of Salpa is subject to periodical and 

 somewhat regular reversal of its direction, the heart has been made 

 the subject of especial study by numerous observers ; but owing to its 

 delicacy and transparency and to its rapid pulsation, its structure and 

 mode of action have never been correctly described, and can be made 

 out only by studying the living animal after it has been treated 

 with ether until the contractions have grown very feeble and slow. 



It consists of three concentric saddle-shaped portions, of which the 

 upper (Fig. 7, 4) and the lower (3) are thick and inflexible, while the 

 middle one (-:") is thin and composed of parallel rows of muscles, which 



* Leuckart, pp. 33 -3S, devotes considerable space to this subject. 



