248 E. W. MACBRIDB. 



of the metamorphosis. In fig. 72 the adult mouth is formed, 

 and the sessile mode of life has been given up, the stalk 

 being reduced to a small solid rudiment. We see also the first 

 trace of the eye as a small knob at the base of hydrocoele 

 lobe No. 3. Fig. 78 shows the permanent anus ; if we com- 

 pare its position with that which the larval anus occupied, we 

 find that they are by no means the same: the larval anus, if it 

 had persisted, would be situated at the point x , though both 

 occupy a position on the mesentery dividing the left from the 

 right posterior coeloms. Fig. 77 from the same larva shows 

 that the left posterior coeloni now forms a complete ring by 

 the breaking down of the partition between its right ventral 

 and right dorsal horns {I'p'd . and l"p"c".). 



In fig. 73 a dorsal section, and in fig. 74 a ventral section, 

 we see the incipient bifurcation of the right posterior coelom in 

 order to form the outgrowths connected with the two dorsal and 

 the ventral pyloric cseca respectively. We see, therefore, that 

 of the five pyloric caeca, two are formed from the dorsal end 

 of the pyloric sac or larval stomach, and two from its ventral 

 end, and that their suspensory mesenteries are outgrowths from 

 the mesentery separating right and left posterior coeloms. The 

 fifth caecum is directed dorsally and posteriorly. In PI. XV, fig. 

 82, and PI. XVI, figs. 83, 84, we have three sections parallel to 

 the adult plane of a specimen which had just completed the 

 metamorphosis. Once the mouth is open, the trifid form of the 

 adult oesophagus changes, we get the five slightly bifid lobes of 

 the adult " stomach." In fig. 83 we see the first trace also of 

 the bifurcation of the pyloric caeca ; I remind the reader that 

 in each arm of the adult there are two caeca; the characteristic 

 appearance of the axial sinus, stone-canal, and right hydrocoele 

 in a section parallel to the disc are also shown, the right hydro- 

 coele having a crescentic form. Fig. 84 shows us the relation 

 of the rectum and the rudiment of the rectal caecum to the 

 pyloric caeca; we see that the mesentery which binds the 

 bases of tlie pyloric caeca together is only the original mesentery 

 between the right and left posterior (oral and aboral coeloms); 

 and, further, that the mesenteric band connecting the inter- 



