236 



s. GOTO. 



2/3 and 3/4 arise at nearly the same time, viz., between stages 

 E and F, but diverticulum 1/5 is formed for the first time in 

 stage F, and remains considerably smaller than the other three 

 (fig. 14 e). These four diverticula together with the posterior 

 extension of the anterior cœlom do not, however, according to 

 my observations, form the whole perihsemal system of authors, 

 but only the circular enterocœl and the central portion of the 



perihsemal system {mihi). In the 

 accompanying cut I have dis- 

 tinguished the enterocœlic por- 

 tions by stippling ; and the 

 portion left vacant arises from 

 the mesenchyme. Let us now 

 follow the changes which the 

 diverticula undergo during meta- 

 morphosis, and to do this it will 

 only be necessary to describe the 

 changes which one of them passes through, as each repeats ex- 

 actly the same process. 



Each out-pocketing arises single, but its distal end, i. e. the 

 blind end, soon begins to be produced in two horns, which 

 then grow out towards the two adjoining interradii, and each 

 horn finally comes to lie between the ectoderm and the hydro- 

 cœlic pouch {cf. fig. 11 c & d). 1'he horns together with the 

 portion adjoining them are afterwards (in stage F/Gr) cut off 

 from the rest by the formation of a septum, and give rise to 

 the outer perihsemal ring of authors and the small central por- 

 tion of the radial perihsemal space stippled in cut 1. In the 

 madreporic interradius exactly similar changes occur, with the 

 only difference that the diverticulum is represented by the 



