W. K. BROOKS ON THE GENUS SALPA. 133 



water. In sunlight the luminous organs have a tinge of purple, but at 

 night their light is as white as the glow of an incandescent wire. 



Sections show that each organ consists of an aggregation of blood 

 corpuscles in a sinus or dilation of the blood spaces of the body cavity. 

 As most of the corpuscles are swollen, irregular, granular, and in process 

 of degeneration, the sections seem to indicate that the degeneration of 

 the corpuscles is the source of the light, although we cannot look for 

 much information on this point from dead specimens. 



Since the time of Savigny, Pyrosoma has been known to have a pair 

 of elongated organs on the sides of the pharynx near the mouth, and as 

 in the case of Salpa, there has been much vague speculation as to their 

 nature. 



Savigny thought they were ovaries ; Huxley suggested that they 

 were kidneys, and Keferstein and Ehlers believed that they might be 

 organs for the production of buds. According to Herdman (p. 22), 

 Panceri first showed that they are really organs for the production of the 

 light for which Pyrosoma is so famous and from which it gets its name. 



Salensky's account of the development of these organs (17), p. 48, 

 and his figure, Taf . 7, Fig. 59, Lzgr, seem to show clearly that, in Pyro- 

 soma, as in Salpa, the organs are simply spaces in the body cavity filled 

 with swollen and degenerating cells. 



This point of agreement between Salpa pinnata and Pyrosoma, while 

 in itself of little weight, must be regarded as a part of the evidence of 

 their relationship. 



Ussow discovered and Bolles Lee has more fully described in the 

 aggregated form of Salpa, a pair of sensory ectodermal tentacles situated 

 near the mouth, and Salensky (17), p. 28, finds in Pyrosoma a pair of 

 tentacles which exhibit a general similarity to those of Salpa, and thus 

 add a little to the weight of the evidence from other sources ; although, 

 inasmuch as Salensky's figures and description show that they are at the 

 posterior end of the body in Pyrosoma, we cannot give unqualified assent 

 to his statement that they are identical with the sense tentacles of Salpa 

 in form and structure as well as position. 



The opinion that Salpa and Pyrosoma are closely related does not, 

 however, rest upon these superficial resemblances, but upon their funda- 

 mental identity of structure, although one of the details, the resemblance 

 in their asexual multiplication, is so complete as to be almost enough in 

 itself to establish their affinity. 



Kowalevsky's and Huxley's accounts of the proliferous stolon of 



