432 SALP^E. THEIR AGGREGATION AND LUMINOSITY. 



replaced by a kind of valve, which permits the entrance of water 

 and prevents its return. By thr constant action of the respi- 

 ratory apparatus, a considerable degree of locomotive power is 

 obtained for these animals, without any special apparatus for the 

 purpose. There do not appear, however, to be any sensory organs 

 by which the animals can be directed towards their food ; and 

 we can scarcely suppose, therefore, that their movements are 

 governed by an intelligent will. 



982. The Salpse are most abundant in tropical climates. 

 Messrs. Quoy and Gaimard relate having seen on one occasion, not 

 far from the Cape of Good Hope, long zones of a reddish-brown 

 colour traversing the surface of the ocean, as far as the eye could 

 reach. These were found, on examination, to consist of minute 

 Salpae, each not more than two or three lines in length, aggre- 

 gated together in bands. The colour was given by their nuclei, 

 which did not exceed millet-seeds in size. These bands are 

 driven through the ocean by the action of the waves ; and they 

 seem to have a remarkable power of preserving their continuity, 

 even when a considerable force (for animals of such delicacy) is 

 applied to separate them. In fact, the connection is so strong in 

 some species, that it is easier to tear the animals themselves than 

 to part one from another ; although their union is accomplished 

 only by the adhesion of their surfaces, or of little suckers, adapted 

 to meet each other, and not by any structural connection. In 

 other species, the adhesion is less powerful ; so that when a mass 

 is placed in a vessel of water, and the sides of it are smartly 

 struck, the individuals fall asunder. 



983. Nearly all of the Salpcz are phosphorescent, or self- 

 luminous ; and the small aggregate species are usually more so 

 than the large isolated ones. The bands which they form are, 

 consequently, among the most brilliant of those luminous tribes, 

 which occasionally give such a sparkling lustre to the waters of 

 the ocean. The Salpse, when thus chained together, produce the 

 effect of long ribands of fire, sometimes drawn straight in 

 direction of the currents, sometimes twisted and almost doubl 

 by the action of the waves. One of the most brilliant combina- 

 tions of Salpae, however, is that which forms the Pyrosoma. This 



