. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. TUNICATA. 1237 mother, the stolon is constructed to admit a proportional quantity of the vital fluid. Two vessels traverse it throughout its length, one proceeding from the anterior extremity of the maternal heart, and the other from the oppo- site end. Hence the blood, forced into one of these vessels by the contraction of the heart, returns by the other ; and at each time the heart commences to contract in an opposite direction, the two vessels quickly coincide in the change. M. Milne Edwards has demon- strated that th
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. TUNICATA. 1237 mother, the stolon is constructed to admit a proportional quantity of the vital fluid. Two vessels traverse it throughout its length, one proceeding from the anterior extremity of the maternal heart, and the other from the oppo- site end. Hence the blood, forced into one of these vessels by the contraction of the heart, returns by the other ; and at each time the heart commences to contract in an opposite direction, the two vessels quickly coincide in the change. M. Milne Edwards has demon- strated that the proliferous stolons of the so- cial and compound Ascidians are likewise traversed by two similar vessels, one of which has an ascending current of blood, and the other a descending current. In examining the stolon at a more advanced period of its growth, one may embrace at a view, owing to the successive germination of buds, the complete series of the phases passed through by each embryo, from the time of its first ap- pearance in the form of a little button, to the lull term of its development (Jig. 788.). The Fig. Salpa zonaria (aggregate) in itsfcetat state. Magni- fied about 4 times. {After Eschricht.') a, b, part of the first set of the young Salpaj; c, d, the second set; e,f, the third set; g, the stem with its germs; h, //, the anterior orifices; i, i, vis- cera ;j,j, ganglia; ft, k, posterior orifices ; I, ves- sels ; m, muscular bands of the branchial sacs. phases passed through by the different organs correspond to those that the same organs present during the development of the " iso- lated "foetus.* Development of the foetal "aggregate" Salpa; within the "; — Whatever may be the mode of aggregation of the associated Salpae at the adult age, their germs are always dis- posed in the same pattern along the stolon in two parallel rows, so that the germs alternate one with another. It necessarily follows that the embryos
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