68 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



at his disposal, he did not feel justified in mutilating a specimen to such 

 an extent as to expose this wall sufficiently to make him realize its 

 unique chai-acter. It shuts the cavity of each ray off from the cavity of 

 the disc completely, the only communication between the two being a 

 small foramen through which the duct of the digestive gland passes. I 

 have found no trace of any such wall in any other starfish which I have 

 examined, and, although further investigation may show that it is not 

 unique, it is undoubtedly the most striking feature of the internal anat- 

 omy of Heliaster. It is easy, however, to see how such a wall might 

 have developed, for, with the coalescence of the rays and the consequent 

 doubling of the interbrachial walls, it would be natural that a stronger 

 union between the rays and disc should arise by the expansion of the 

 proximal ends of those walls. The subsequent increase and coales- 

 cence of such expansions would readily follow, thus giving a very un- 

 usual, but necessary, strength to what would otherwise be a line of 

 weakness. — The further examination of the internal anatomy of Heli- 

 aster reveals some interesting similarities with Asterias, which have not 

 been noted hitherto. The reproductive organs occupy the same position 

 as in that genus, and are identical in form, so that the only difference is 

 in the actual number of gonads, there being a pair in each ray in both 

 genera. The form and position of the stone-canal and the axial organ 

 are identical in the two. The racemose glands (Tiedemann's bodies) a,re 

 similar in form and position, but are much more numerous in Heliaster 

 than in Asterias, ranging from 10 to 26 in the twelve specimens of 

 kubiniji and polybrachius examined. They do not show any regularity 

 in position, however, or any correlation between their number and the 

 size of the individual, or the number of rays. The digestive system of 

 Heliaster (Plate 7, fig. 1) is surprisingly like that of Asterias in spite 

 of the separation of the disc cavity from the rays. The stomach is very 

 capacious, and is obviously pushed out of the mouth in feeding, just as 

 in Asterias, and (as already mentioned on p. 59) its five pouches are 

 each attached by a pair of strong muscles, as in that genus, to the am- 

 bulacral plates of the basal part of a ray. These muscles pass from the 

 stomach through the openings in the discobrachial wall (which are per- 

 haps a trifle larger in these rays) used by the ducts of the digestive 

 glands. This pentamerous symmetry of the stomach-muscles is most 

 striking, and it can hardly be doubted that it i-eveals a close relation- 

 ship to Asterias. The intestine is short, and bears the customary 

 rectal gland, which consists, as in Asterias, of several much divided 

 branches. 



