Ill THALIACEA (SALPIANS) 95 



some years later (Perrier's P. excelsior) by the French " Talisman " 

 expedition in the tropical Atlantic. The late Professor Moseley 

 said of this (" Challenger ") species, " I wrote my name with my 

 finger on the surface of the giant Pyrosoma as it lay on deck in 

 a tub at night, and my name came out in a few seconds in letters 

 of fire." Bonnier and Perez have recently recorded that they 

 saw an enormous profusion of a large Pyrosoma (up to four 

 metres in length) in the Arabian part of the Indian Ocean. 



Order III. Thaliacea (Salpians). 



Free-swimming pelagic forms of moderate size, which may be 

 either simple or compound, and in which the adult is never 

 provided with a tail or notochord. Consequently the whole body 

 here corresponds to the trunk only of the Appendicularian with- 

 out the tail. The test is permanent, and may be either well 

 developed or very slight. In all cases it is clear and trans- 

 parent. The musculature of the body -wall is in the form 

 of more or less complete circular bands, by the contraction of 

 which water is ejected from the body, and so locomotion is 

 effected. The branchial sac has either two large, or many small, 

 stigmata, leading to a single peribranchial cavity, into which 

 the anus also opens. Blastogenesis takes place from a ventral, 

 endostylar stolon. Alternation of generations occurs in the 

 life-history, and may be complicated by polymorphism. The 

 Order Thaliacea comprises two groups, Cyclomyabia (such as 

 Boliolum) and Hemimyakia (such as Salpa). 



Sub-Order 1. Cyclomyaria. 



Free-swimming pelagic forms which exhibit alternation of 

 generations in their life-history, but never form permanent 

 colonies. The body is cask-shaped, with the branchial and atrial 

 apertures at the opposite ends. The test is moderately well 

 developed, never much thickened. The musculature is mostly in 

 the form of complete circular bands surrounding the body. The 

 branchial sac is fairly large, occupying the anterior half or more 

 of the body. Stigmata are usually present in its posterior part 

 only. The peribranchial cavity is mainly posterior to the 

 branchial sac. The alimentary canal is placed ventrally, close to 



