ASEXUAL REPRODUCTION. 



99 





The stolon is formed by the simple growth of the two germ-layers 

 present in the peduncle, i.e., the ectoderm and the mesenchyme 

 (HARMER, SEELIGER). Consequently the buds formed on the stolon 

 also owe their origin exclusively to these two germ-layers. HATSCHEK'S 

 view that, in addition to these constituents, an entoderm-sac also 

 enters into the formation of each bud, this sac having arisen by 

 abstriction from the mid-gut rudiment of the next older individual, 

 must, according to HARMER and SEELIGER, be regarded as erroneous. 

 According to these two authors, the formation of the buds recalls 

 that of the 

 polypides of 

 the Ectoprocta. 

 The first rudi- 

 ment of the 

 bud is a bulging 

 caused by the 

 growth of the 

 two germ-layers 

 (Fig. 47 A, st), 

 an ectodermal 

 invagination 

 soon forming at 

 the apex of this 

 swelling (Fig. 

 47 B). The sac 

 which has thus 

 -arisen soon be- 

 comes divided 

 by constriction 



into two parts (Fig. 47 A\ the larger outer part representing the 

 rudiment of the vestibule (a), and the smaller inner part that of 

 the whole alimentary canal (i). In this case, as in the Ectoprocta, 

 the mid-gut has not an independent entodermal origin. The point 

 at which communication between the two parts of the sacs is retained 

 becomes the future oral aperture, while the development of the hind- 

 :gut and of the anal aperture follows only later. In this respect the 

 formation of buds in the Entoprocta deviates from that in the 

 Ectoprocta, where the anal communication of the vestibule with 

 the mid-gut is the first to be established (p. 40). An ectodermal 

 invagination which forms at the base of the vestibule, between the 

 oral and anal apertures, gives origin to the ganglion, which, as a 



FIG. 47. Budding in Pedicellina (after SEELIGER). A, portion of a 

 stolon with a very young rudiment of a bud (st) and an older rudi- 

 ment in which can already be seen the separation of the vestibule 

 (a) and the intestinal rudiment (i). B, bud, with simple polypide- 

 invagination (p, common rudiment of the vestibule and the 

 alimentary canal), a, vestibule ; ec, ectoderm ; i, rudiment of 

 intestine ; ms, mesenchyme : o, mouth ; p, polypide-rudimeut ; 

 st, young bud-rudiment. 



