. Elements of Comparative Anatomy. VASCULAE SYSTEM OP TUNICATA. 405. to a vessel. One of these two vessels taking a ventral course breaks up into a net-work which, is distributed over the branchial lattice- work, whilst the other passes to the intestine and to the generative organs and branches out upon them. The same main-vessel sends also a branch to the mantle and twigs to the wall of the coelom (body-cavity). The blood distributed in this set of vessels is col- lected again into a longitudinal trunk lying on the dorsal side of the branchial sac, which also receives vessels from the intesti
. Elements of Comparative Anatomy. VASCULAE SYSTEM OP TUNICATA. 405. to a vessel. One of these two vessels taking a ventral course breaks up into a net-work which, is distributed over the branchial lattice- work, whilst the other passes to the intestine and to the generative organs and branches out upon them. The same main-vessel sends also a branch to the mantle and twigs to the wall of the coelom (body-cavity). The blood distributed in this set of vessels is col- lected again into a longitudinal trunk lying on the dorsal side of the branchial sac, which also receives vessels from the intestine and from the generative organs. Whether these dispositions which have been observed in the solitary Ascidians have a more general distri- bution is not yet ascertained. In the Salppe the short, thin-walled heart (Fig. 212, c), generally having the form of a tube, constricted at intervals, is in connection with a large vascular canal (y), which runs along the ventral surface, and also at the opposite end the heart is directly continuous with a large vessel; the latter, in those forms which possess a so-called nucleus {vi), breaks up at once into a reticular system, which is distributed in this body, and represents the intestinal ves- sels of the Ascidians. In other Salpte (those without nucleus) it appears to divide into many branches, which run towards the dorsal surface and end in a longitudinal canal. This dorsal vessel (y') is placed in communication with the ven- tral stem by a number of ti-ans- verse canals {v), which freely anastomose with one another. There exists a further direct communication between the anterior portion of the dorsal vessel and the hinder vessel proceeding from the heart, through a number of vessels which run through the gills and break up there. The most important peculiarity of the vascular system of the Tunicata is assuredly the existence of the two longitudinal stems which pass along the branchial sac, and which farther on meet on the intestine
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