I l6 C. M. CHILD. 



else. It is evident from Figs. 17 and 24 that they arise in con- 

 nection with intermesenterial chambers, for the lines extending 

 aborally from the bases of the oral tentacles represent grooves 

 marking the lines of attachment of the mesenteries to the cesoph- 

 agus. Moreover, Fig. 24 shows that the aboral tentacles arise 

 from those intermesenterial chambers which are least contracted 

 for the only intermesenterial chambers which are at all distended 

 at the aboral end are those from which the aboral outgrowths 

 arise. In these respects these structures resemble the normal 

 tentacles, and these facts lend color to the view that the condi- 

 tions of origin of these aboral tentacles are similar to those of the 

 normal tentacles. 



In Figs. 19-23 and 2628 the course of the intermesenterial 

 circulatory currents is represented by arrows. These pass orally 

 along the body-wall and aborally along the oesophagus. In 

 both pieces the aboral end of the oesophagus bulges outward 

 just oral to the line of union with the body-wall. 



From Figs. 20 and 27 it is seen that this condition presents an 

 obstruction in the course of the current in the aboral direction 

 along the oesophagus, /. c., local pressure upon the wall may 

 occur. Except that they are reversed in position conditions here 

 do not differ essentially from those described above leading to 

 the formation of supplementary discs in the middle region (see 

 Figs. 1214). In brief, the suggestions regarding local pressure 

 due to circulatory currents are as readily applicable to these 

 cases as to the normal oral tentacles. Moreover, there is no 

 adequate explanation on any other basis for the fact that these 

 aboral tentacles arise from cesophageal tissue, or from the line of 

 union between oesophagus and body -wall, rather than from the 

 body-wall, like tentacles at the oral end. In my opinion the 

 occurrence of these heteromorphic tentacles constitutes another 

 important piece of evidence in support of the views already set 

 forth (Child, '04$, '04^). The case of the single large tentacle 

 which arose from the new tissue at the union of oesophagus and 

 the folded body-wall (Fig. 25) is peculiar. The size of the ten- 

 tacle is probably due to the greater distance between mesenteries, 

 itself the result of stretching or growth of the new tissue at this 

 point. The impossibility of ascertaining the exact internal con- 



