40 



ZOOLOGY 



SECT. 



the parent Doliolnm (Fig. 738) loses its branchiae, its endostyle, 

 and its aliniontary canal ; at the same time the muscle-bands 



dors.st 



yrapi 



enih 



vent st 



Fig. 738. — Soliolum, lateral view of asexual stage, showing the early development of the buds. 

 air. 11)1. atrial aperture ; dors. st. eadoi)hore ; e. embryos passing over the surface from the 

 ventral stolon to the cadophore ; lit. heart ; ne. i/n. nerve-ganglion ; or. ap. oral aperture ; 

 vent. St. ventral stolon. (After Uljanin.) 



increase in thickness and the nervous system attains a higher 



develojmient, until the Avhole parent 

 comes to play a part like that of 

 the nectocalyx of a Siphonophore 

 (Vol. I., p. 159), its exclusive function 

 being by its contractions to propel 

 the colony through the water. 



The zooids of the cadophore 

 consist of two sets, differing from 

 one another in position and in 

 future history — the lateral zooids 

 and the median zooids. The lateral 

 zooids serve solely to carry on the 

 nourishment and respiration of the 

 colony, and do not undergo any 

 further development. Some of the 

 median buds, on the other hand, 

 become detached and take on the 

 special character of phorozooids. 

 When free, each phorozooid carries 

 with it the stalk by means of 

 which it was attached to the stolon ; 

 on this stalk there have previ- 

 ously become attached a number 

 of buds which are destined after 

 a time to be developed into the 

 sexual zooids. 



The succession of stages in the 

 life-history of Doliolum thus bi-ietlv 

 sketched will be seen to .succeed 

 one another jn the i'oUowing 



dor 



.btZs 



/ned.bds 



Fig. 739.— Doliolum, dorsal view of 

 the posterior part of the body of an 

 asexual zooid, showing the cour.se 

 taken by the buds (cnt'i.) over the sur- 

 face from the ventral stolon (renf. 

 stol.) to the cadophore (dors. atoL) and 

 their growth on the latter, lal. hds. 

 lateral buds ; mal . hiU. median buds ; 

 im-ic. pericardium. (After Carrois.) 



