ON DEVELOi'.MEXï ETC. Oi' i'llUllONJS. OiO 



ions, is drawn out into a lonii' tube, and at the next moment 

 the junction of the stomach and the intestine is lirst of all 

 pushed into the now s])aeious pouch. Thus, the aims and ten- 

 tacular region are In'ought into close approximation on the dorsal 

 line of the tiunk ; the digestive canal folds hack on itself into an 

 U-sha])ed tube, as we lind it in the adult. The larval tentacles 

 and the ])reoral lobe are cast off and digested in the stomach; the 

 perianal <'iliated belt atrophies i/i situ. It is during this moment 

 that the corpuscular masses break away and their elements are 

 scattered in the blood vessels, some of which are then being formed. 

 It is highly interesting to observe the l)reaking up of the corpus- 

 cular masses, and the motion of the corpuscles in consequence of 

 the I'hythmical contraction and expansion of the dorsal vessel and 

 of the cu'cal capillaries. The deep pinkish colour of the corpuscles 

 makes it easy to observe their progress into the vessels. Ordi- 

 narily after about twenty minutes the vasctdar system of the 

 worm is completely formed and the circidation characteristic of 

 riioroiiU can be noticed. The .-kin of the foot Avhich now forms 

 the princij>al part of the Innly, becomes more opaque on accoimt 

 of the secretory products from the innumerable unicellular glands. 



To understand the details relating to the metamor])hosis we 

 nuist examine the animal in sections. Figs. (>4 {o-d) show a dis- 

 continuous series of cross sections of the lai'va represented in lig. 11, 

 which is a})proxiniately at the critical moment of metamor])hosis. 

 I will briefly sketch with the aid of these iigures the general 

 internal change during metamorphosis. 



Eniohladic Organ<. When the ventral pouch is fully evagi- 

 nated and the stomach is ptished into the poiu-h, the (.esophageal 

 portion elongates downwards enormously, so that the stomach 

 diverticulum descends far below the postoral septiuu, that is to say, 



