40 



ZOOLOCV 



the parent Doliolum (Fig. 73.S) loses its Ijmnchiie, its cndostyle, 

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



"^^7/? ,lnrs.st 



— aZr.a.p 



z'^nt st 



Fic;. 73^;. — Doliolutn, lateral view uf asexual stage, showiug the early develoi'ineiit uf the hirls. 

 aU\ ap. atrial aperture ; dors. .it. cadophore ; e. embryos passing uvcr the surface from the 

 ventral stolon to the cadophore; hf. heart; He. <j'a. nerve-ganglion; or. ap. oral aperture; 

 rent. 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 Siphono|)hore 

 (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 

 c<jlony, and do not undergo any 

 further dc\-elopinent. Some of the 

 median buds, on the other hand, 

 bec(.)me 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 ; 

 nil this stalk there have previ- 

 ously become attached a number 

 of buds which are destined after 



^ a time to tic de\'eloped into the 



1 K(.'xua.l zooids. 



: The succession of stages in the 



j life-history of DoJioJuni thus briefly 

 sketched will bi; seen to succeed 

 one another in the followinsf 



Irtt.hdb- 



al \ieu' 

 i.ly of : 



Fio. 7a;i.— BoUolum, d. 



the posterior p.irt "f t]i 

 asexual zooid, sinewing the 

 taken by the buds fcj/t'j.) over the sur 

 face from the ventral stolon (ri'/// 

 stot.) to the cadophore {dors .^tol.) .mi 

 their growth on the latter, lul. tuts 

 lateral buds ; nod /<>/„■. median liuds 

 l^rir. pericardium. (After Barrels. ) 





