THALIACKA. 107 



and the mother, and this structure plays an important part 

 in the nourishment and growth of the embryo. In the further 

 development of the organs, which agrees in its general features with 

 that of the Ascidians, the placenta becomes more sharply marked off 

 from the body of the embryo, at the posterior end of which a 

 structure known as tin- elceoblasttihe equivalent of the notochord 

 makes its appearance (fig. 567 c). 



It is only after a Relatively long period that the embryo is born as 

 a small fully- developed Xtd/>K, which, however, still possesses the 

 remains of the placenta and the rhi'oblast. 



This solitary Saljxt, which has been produced sexually, grows 

 considerably during its free life, but always remains asexual, while 

 by budding on its stolon it produces a number of individuals united 

 together in chains. This stolon or germ-stock is a process of the 

 body containing the rudiments of the most important organs. Its 

 central cavity is traversed by a stream of blood, and on its walls 

 the buds sprout out. In Salpa, as in the Ascidians, the stolon lies 

 on the ventral side, and later enters into a special, open excavation of 

 the body covering (fig. 567 a). 



On account of the extraordinary fertility of the stolon several 

 groups of buds of different ages are always present one behind the 

 other ; they separate successively as independent chains. 



In Doliolum the reproductive processes are much more complicated, 

 for not only do the sexually produced young undergo a metamorphosis 

 but a new series of generations is introduced into the life history. 

 The eggs are laid, and the larva; which issue from them are provided 

 with tails and resemble Ascidian larva? (fig. 568, e). They develop 

 into asexual forms which differ from the sexual forms, and are pro- 

 vided with a dorsal stolon (fig. 568 b, Std} ; the ventral stolon (stolon 

 of Salpa) is rudimentary (<SVr) (rosette-shaped organ). Two different 

 kinds of buds are formed on this dorsal stolon, viz., median buds and 

 lateral buds (Gegenbaur). The lateral buds have a slipper-like form, 

 and are without the cloacal cavity ; they do not reproduce themselves, 

 but are concerned with the nourishment of the asexual form. The 

 latter as it increases in size loses its gills and alimentary canal, 

 Avhile its muscular system becomes powerfully developed. The 

 median buds develop into individuals, which resemble the sexual 

 animals except.that they are without genital organs ; they therefore 

 represent a second generation of asexual forms, which become free and 

 produce the sexual generation from a ventral stolon. 



