I] 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 Pérez 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, CYCLOMYARIA (such as 
Doliolum) and HEMIMYARIA (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 
