390 



ZOOLOGY 



SECT. 



in such a way as to give rise to the coelome of the adult. The 

 anterior undivided part (anterior coelome} forms the coelome of a 

 conspicuous larval structure, the pre-oral lobe, and it eventually 



'larv.org 



iarv.oig 



e&, 



arch, 



FIG. 314. Later stages in the development of the larva of Asterina gibbosa A, newly 

 hatched larva, ventral surface with the beginning of the larval organ at the anterior end and 

 with the larval mouth. B, dorsal half of an embryo of the same age as A. C, somewhat older 

 larva with larger larval organ, the ectoderm of the left side removed to expose the alimentary 

 canal and the walls of the body-cavity, arch, archenteron ; bl. p. blastopore ; ect. ectoderm ; 

 ent. enteroccele ; larv. mo. larval mouth ; Ian: org. pre-oral lobe ; stom. stomodajum. (From 

 Ziegler's models.) 



becomes cut off from the right and left pouches, giving off on 

 the left a five-lobed outgrowth, the hydroaale, which forms the 

 foundation of the entire ambulacral system of the adult : a right 



B ktrv. 



ec 



Fit;. 315. Larva of Asterina gibbosa. A, diagrammatic lateral view ; the alimentary 

 canal dotted, the ambulacral system -striated, the ectoderm shaded. B, Larva seen from the 

 left as ail opaque object, the body-wall of the left side removed ; hydroccele separated off 

 from left enteric sac and partly surrounding oesophagus, all. alimentary canal ; amb. ambula- 

 cra! system or hydroccele ; dors. p. dorsal pore ; <>ht. enteric sacs and coelome ; larv. mo. larval 

 mouth ; larv. org. pre-oral lobe ; oe.<?. oesophagus of adult ; r, r. lobes of hydrociele ; sept. 

 septum between the enterocielic sacs. (A, after Ludwig ; B, from Ziegler's models.) 



hydrocoele is only represented by a small vesicle which in normal 

 embryos undergoes no further development. Before the hydro- 

 coele is developed and before the right and left coelomic 

 pouches have become cut off, two apertures make their appearance 



