Notes on the Adult Anatomy of Solaster endeca. 187 



off from the axial sinus. Then, as a new and somewhat surprising circum- 

 stance, I find that the aboral sinus itself is not continued right across the 

 madreporic interradius but suffers an interruption there, which I think I can 

 hardly be mistaken in saying is quite complete. Two adjacent blind ends are 

 thus produced. In reality their walls are in close apposition to one another 

 below the dorsal sac, although in the figure, for purposes of illustration, they 

 seem to be more widely separated. On the sinistral x side the blind end of 

 the sinus is continued orally down the edge of the interbrachial septum for a 

 considerable distance, running parallel with the axial sinus, but ultimately 

 it becomes smaller and finally disappears before half the distance down the 

 septum has been traversed. 



Each of the blind ends is continued directly into a large genital branch 

 (genital sinus). The two genital sinuses pass outwards on the aboral body 

 wall one on each side of the interbrachial septum, and are continued on to 

 the roots of the corresponding gonads, ending finally in spaces between the 

 inner and the outer layers of the gonad walls (8). 



There is no interruption to the lumen of the aboral perihsemal sinus in 

 any of the other interradii. 



The older teaching (Ludwig, 1, p. 617 ; Cuenot, 2, p. 591) was that the 

 aboral perihsemal ring opened into the axial sinus. Cudnot, however, noted 

 that in Asterias glacialis and Astropecten aurantiacus the communication was 

 by a very small channel. Delage and Herouard (11, p. 57) leave the question 

 open, though on functional grounds they incline to the view that a com- 

 munication ought to exist between these cavities. Macbride has the merit of 

 having first shown that developmentally in Asferina (6) the aboral ring and 

 the axial sinus are unassociated with one another, and in the paper on 

 Asferina to which a reference has just been given (as well as in vol. i. of the 

 Cambridge Natural History), he has described them as being quite separate in 

 the adult starfish. 



However, an interruption of the aboral periluemal sinus in the madreporic 

 interradius does not seem to have been previously noted, and I cannot say at 

 present whether it occurs in any other starfish or is peculiar to Solaster 

 endeca. Developmentally in this species as compared with Asterina, the 

 extension of the genital rachis and of the aboral periruemal sinus seems to be 

 much delayed, although both these structures originate in a similar manner 

 and from corresponding regions of the coelomic wall. Thus in a young 

 Solaster five months after the completion of metamorphosis, the aboral peri- 

 haemal sinus was only traceable for a short distance on the sinistral side of 



1 See note at foot of page 174. 



