DOLIOLIDA. 



59 



G 



a mere swimming organ (Fig. 53), which propels itself through the sea, by 

 expulsion of water from its atrial aperture like a salp, and draws after itself 

 the trailing dorsal stolon with its four rows of developing zooids. 



The median buds 

 develop into phoro- 

 zooids (Fig. 52). 

 These are small 

 doliolum-like crea- 

 tures with long 

 peduncles of at- 

 tachment, with 

 eight muscular 

 hoops and with the 

 rudiments of sexual 

 organs, which how- 

 ever soon disappear. 

 As soon as they 

 have reached full 

 development they 

 become detached 

 and swim freely in 

 the sea. On de- 

 tachment each of 

 them possesses on 

 its ventral peduncle 

 a probud which has 



s - 



FlG. 53. Asexual bud- 

 ding form of Doliolum 

 denticulatum after at- 

 rophy of its alimen- 

 tary organs, showing 

 the trailing dorsal pro- 

 cess with rows of buds. 

 m muscles; ms median, 

 Is lateral buds. 



FIG. 52. Diagram of a dorsal view of the dorsal appendage of 

 Z)oh'otejshowinggastrozooids G, phorozooids P, and probuds g, 

 destined to give rise to the sexual zooids (after Delage and Her- 

 ouard). cl median septum dividing the vascular space of the 

 dorsal process ; ec.s thickened dorsal ectoderm of the dorsal 

 process ; G lateral buds (gastrozooids) ; g probuds which will 

 attach themselves to the peduncles of the phorozooids and form 

 sexual zooids ; P median buds (phorozooids) ; pi placenta-like 

 connection of ectoderm of bud to ectoderm of dorsal process ; s, s 

 vascular cavity of dorsal appendage. On the left side of the 

 figure the stalks of the three last gastrozooids only are shown. 

 The phorozooids of the left side are shown in longitudinal section, 

 as is the last gastrozooid but one on the right side. The others 

 are shown in external view. 



travelled on to it from the dorsal process. This 

 probud divides into from fourteen to twenty buds 

 which attach themselves in the usual way to the 

 pedimcle of the phorozooid. Here, during the free- 

 swimming life of the phorozooid, they develop into 

 the sexual form. The sexual form then belongs to 

 the same generation as the gastrozooid and phoro- 

 zooid. These three forms are all produced by bud- 

 ding from the ventral stolon of the asexvial form 

 which arises from the egg. 



To sum up the matter, the life-history of 

 Doliolum is an example of the alternation of 

 an asexual budding generation which proceeds 

 from the egg and of a polymorphic genera- 



