ANATOMV AND PHYSIOLOGY OF SALPA AND PYROSOMA 63 



On the other hand, in Pelonaia the hypopharyngeal band itself has 

 disappeared. It is a Salpa in which the oral and cloacal orifices have 

 approximated while the " gill " has become obliterated.* 



In the strange form Appendicularia (79), the simplification is carried 

 a step further, for there is but one orifice, the oral. The anus opens 

 on the dorsal surface, and a long appendage is added in the same 

 position as that of Boltenia, but instead of being a long pedicle of 

 attachment, it is a free and energetically moving fin. 



67. To sum up what has been said, it appears that the Salpa; are 

 not, as has been generally supposed, an aberrant form of the Tiimcata, 

 but rather that they are connected by insensible gradations with the 

 other forms of the group ; neither is there any circumstance in their 

 two modes of multiplication at all at variance with what takes place 

 in other genera of the family. 



The distinction between monochitonidous and dichitonidous Tuiii- 

 cata cannot be kept up in its present sense, for the proper inner and 

 outer tunics are equally adherent in all Tunicata ; and as expressing 

 the degree of adherence of the test to the outer tunic, the distinction 

 is of no value, systematically, as the character may vary greatly in 

 the same or closely allied genera. 



Section IV. — History of our Knowledge of the Salpa;. 



68. Forskahl, the Danish naturalist, founded the genus Salpa upon 

 certain animals taken in the Mediterranean. No less than eleven 

 species are described and figured by him (and with remarkable clear- 

 ness and accuracy) in his " Descriptiones Animalium," a work which 

 he unfortunately did not live. to see published, but which made its 

 appearance in the year 1775. 



The following is a definition of the genus : " Salpa corpore libero, 

 gelatinoso, oblongo, utroque apice aperto ; intus vacuo ; intestino 

 obliquo variat : a) nucleo globoso, opaco, juxta anum b) nucleo nullo 

 sed linea dorsali opaco. 



" Nomen mutuatum a 'ZoKira, pisce a Graecis cognito et huic vermi 

 additum ob similitudinem formse cum tubo canoro. Animal plerumque 

 gregarium ; mira cohaerens symmetria motum corporis per systolem 

 et diastolem, siphonica arte perficiens." 



Browne,^ who appears to have been unacquainted with Forskahl's 



^ Chelyosoma would appear to resemble Pelonaia in the absence of any distinct branchial 

 sac ; but Eschricht's figures are not very clear. 

 ^ Natural History of Jamaica, 1785. 



