MUSEUM OF COMPARATIVE ZOOLOGY. 



!23 



The Muscles. — The bands of the two sides of the body are at first 

 entirely distinct from each other, as noticed by Krohn, and all of those 

 upon one side are, at first, united above and below, as in Fig. 23 ; the 

 haemal ends of the first, second, third, and sixth, in the solitary Salpa, 

 soon become free, as shown in Fig. 24, and the neural ends separate 

 into two bundles, composed of the first, second, third, fourth, fifth, 

 and sixth, respectively (Fig. 24). The first now separates at both 

 ends (Fig. 25), and after a time the haemal ends of the fourth and 

 fifth also become free, but the amount of separation is not uniform 

 in specimens of the same age, and the union between the fourth 

 and fifth may persist until the animal is nearly full grown (Figs. 

 1, 2, and 23); and to this the discrepancy in the various descrip- 

 tions of the species is due. The neural ends of all the corresponding 

 bands upon the two sides of both forms of Salpa soon unite, as well 

 as the haemal ends of the first, second, third, fourth, and fifth of the 

 solitary Salpa, which thus form closed muscular belts or girdles en- 

 circling the body ; while the luemal ends of the sixth pair of the 

 solitary Salpa, and of all in the chain-salpa, are permanently free. 

 Soon after the muscular layer begins this process of division, it ad- 

 Fig. 25. 



Solitary Salpa, — female, at the time when it escapes from the body of the male, viewed from the 

 side, with the neural surface uppermost: a, test ; h, outer tunic; d, digestive organs; c, 

 branchial aperture ; g, atrial aperture ; h, branchial cavity; i, atrial cavity; I, epipharyngeal 

 fold ; m, endostyle ; n, gill ; p, placenta ; u, stolon ; v, ganglion ; w, languette ; x, elaeoblast. 



heres to the inside of the outer tunic, in which situation the muscles 

 of the adult are always found ; and this tunic has accordingly been 

 called the muscular tunic, although, as we have seen, the muscles 

 really belong to the atrial portion of the body. The muscles of the 



