The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . lony. Thus thereis alternation of generations in the life-history. In the most completely formedcolonies (eg., Botryllus) the ascidiozooidsare arranged in groups (systems or coeno-bii), and in each system are placed withtheir atrial apertures towards one another,and all communicating with a commoncloacal cavity which opens to the exteriorin the centre of the system (fig. 19 Di)
The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . lony. Thus thereis alternation of generations in the life-history. In the most completely formedcolonies (eg., Botryllus) the ascidiozooidsare arranged in groups (systems or coeno-bii), and in each system are placed withtheir atrial apertures towards one another,and all communicating with a commoncloacal cavity which opens to the exteriorin the centre of the system (fig. 19 Di). Sub-order 3.—Ascidise Salpifonnea. Free-swimming pelagic colonies having ?^^2^(^M^f^^ ^ Ascidim the form of a hollow cylinder closed at one ^ ^ v Salpi- end. The ascidiozooids forming the colony aO—Pj/rosoma ehgansj<^^-are imbedded m the common test in such a natural size. A. Side viewmanner that the branchial apertures open of entire colony. U. Endon the outer surface and theatrial apertures (OrTRinal ^^^^ extremity,on the inner surface next to the central cavity of the colony. The ascidiozooids are produced by gemmationfrom a rudimentary larva (tho cyathozooid) developed sexually. XXIIL — 78. 618 T U N I C A T A Etnic- This snb-order includes a single family, the Pyrosomidj:, con- tare o taining one well-marked genus, Pyrosoma (Peron), with severalPyro- species. They are found swimming near the surface of the sea,soma. chiefly in tropical latitudes, and are brilliantly phosphorescentA fully developed Ptjrosoma colony may be from an inch or two toupwards of four feet in length. The shape of the colony is seen in6r. 20. It tapers slightly towards the closed end, which is opening at the opposite f nd is reduced in size by the presenceof a membranous prolongation of the common test (fig. 20, B).The branchial apertures of the ascidiozooids arc placed upon shortpapills projecting from the general surface, and most of the ascidio-zooids have long conical
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