40 



ZOOLOGY 



SECT. 



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

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



or.ap 



alr.a-p 



peric 



vent st 



FIG. 738. Doliolum, lateral view of asexual stage, showing the early development of the buds. 

 atr. ap. atrial aperture ; dors. st. cadophore ; e. embryos passing over the surface from the 

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

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



increase in thickness and the nervous system attains a higher 



development, until the whole 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 

 tjtie 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 pJiorozooids. 

 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 



FIG. 739. Doliolum, dorsal view of . , 



the posterior part of the body of an SCXUal ZOOlQS. 



^nVtt d budtSfovt^rsur- The succession of stages in the 

 l!S!) tothe cadophoretrfo S rs 0l So? fand life-history of Doliolum thus briefly 



their growth on the latter! lat. Ms. sketched will be S66n 'to SUCCeed 

 lateral buds ; med. bds. median buds; ,1 0.1 r- n 



peric. pericardium. (After Barrels.) One anotiier in the following 



dors.slol 



lal.bds 



