METAMORPHOSIS OF ASTERINA. 



147 



growth of the adult oeso- 

 phagus and the formation 



of the new mouth on the 



left side. 



Even before the meta- 

 morphosis the lobes of the 



hydrocoel are visible on the 



left-hand side of the larva 



in a curve open anteriorly 



(Fig. 102), the dorsal lobe 



being no. 1, the posterior 



no. 3 and the ventral no. 5. 



On the right side are visible 



the first rudiments of the 



arms, lettered A-E, the 



dorsal being A and the ven- 

 tral E ; these arm rudiments 



are developed over the left 



posterior coelom. The open 



curve of the hydrocoel 



eventually closes into a 



circle, the two ends coming 



together round the base of 



the preoral lobe (stalk), so that the preoral lobe arises from 



the oral surface of the developing disc (Fig. 105). In this closure 



the rudiment of arm E shifts so that it comes to lie directly 



on lobe no. 1 of the hydrocoel. 

 When this fitting together of the 

 two surfaces of the future disc is 

 complete, the oral and aboral sur- 

 faces of the starfish are fashioned, 

 and it is seen that the oral surface 

 is derived from the left and slightly 

 ventral side of the larva, the aboral 

 from the right and slightly dorsal 

 side. Meanwhile the first cal- 



FIG. 103. Larva of Asterina gibbosa of i , i . i -, 



nine days from the right side. The CareOUS plates are laid QOWn On 



letters denote the rudiments of the j-i i -, > 



arms, the arabic numerals the lobes of ^ e RDOral SUrlaCC RS SllOWTl in 



the hydrocoel. The first formed tube- TV -,f\j r> t r 



feet have been budded out from the * l g- 1U4: -t>, On the Oral SUriaCC in 



hydrocoel lobes (from MacBride, after TV it\A A mi 7 -11 



Fig. 104 A. The terminals, as will 



FIQ. 102. Larva of Asterina gibbosa at the com- 

 mencement of the metamorphosis (about 

 eight days), a from the left side; b from the 

 right (after Ludwig, from MacBride). The 

 larval organ has disappeared. The arabic 

 numerals denote the primary lobes of the 

 hydrocoel, the letters A-E the rudiments of 

 the arms. 



