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MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES, 95 



McBeidk (10) and Goto (5) both agree that in starfishes the inner perihitmal ring sinus 

 arises from the anterior entorociile, although they differ as to the method of its formation. In 

 none of the larvie 1 have is the structure iu ciuestiou fully formed, but iu Stage "F" a cavity is 

 arising, as an outgrowth from the anterior euteroco'le in the stone (lanal iuterradius, which I 

 take to be the rudiment of the inner perihienuil ring space. It lies to the left of the stone canal 

 uear tlie median sagittal plane of the larva. From the posterior side of the ventral eud of the 

 anterior enterocole the outgrowth takes its origin, then extending posteriorly until past the water 

 ring it bends over and grows down until its end reaches the nerve ring at a point inside the outer 

 perihainal sinus. Uere the end of the pouch in question begins to spread under tiie nerve ring 

 iu both directions, parallel to the outer perihiemal ring (tigs. 24 and 26, ips). This coincides 

 exactly with its method of origin in Asfcrin<i (jibhona as described by McBuide. 



Altliongh the outer perilia-nial ring is entirely cut olf from the body cavities at this stage, 

 there still remain traces of tlie interradial pouches which gave rise to it (tig. 29, hip 1-2 and 4-5). 



The hy])ogastric enterocade itself has changed very little since Stage "E," but the epigastric 

 has enlarged to such an extent that its edges now meet the edges of the hypogastric and a circular 

 aboral mesentery is formed (figs. 23-29, cm). 



In the water system (considerable growth is to be noted in the tentacles, the end and tirst 

 pair of foot tentacles being capable of protrusion considerably beyond the disk, liy means of 

 these tentacles the larva' are able to cling tenaciously to the surfaces of foreign bodies, it requiring 

 a strong Jet of water Iroui a pipette to detach them. Si)ecial notice was taken to be sure that it 

 was the tentacles and not the larval organ which was used as a means of attachment. 



The second pair of tentacles (buccal tentacles) have acquired their ectoderm in this stage and 

 they protrude, like the other tentacles, over the radial nerves into the radial grooves (tigs. 22 

 and 26, t2). 



The axial sinus or ampulla is present in "F," it being that part of the anterior cnteroccele 

 which remains after the pouches have been cut olf, which will form the inuer i)eriha'mal and part 

 of the outer periha-mal systems (tigs. 24, 25, and 26, ax sin). 



It will be noted that beside the ampulla, which is situated anteriorly to the stone canal, there 

 are two other cavities uear the stone canal to be accounted for (lig. 20, sin a and sin b). I can 

 not be sure of their origin, but 1 believe that they also come from the anterior enteroccele. I have 

 distinguished them by the letters a and b, as they are probably the same cavities as those so let- 

 tered by McBride (10) in liis ligures of Aniphiura. 



Tiie cavity McBriue has lettered b', and which ho thinks represents the degenerated right 

 hydrocade, I have been unable to tind in any of my sections. 



The stomach and <eso2)hagus are in a condition the same as we found them iu "E;" that is, 

 without lumen. 



Stage "G," 5 J Days Old. 

 (Figures 31 and 32.) 



Larval a few hours older tiiau " F " show a decided degeneration in the larval organ ( fig. 31, lo), 

 but otherwise the external appearance of the two stages is about the same. 



The grooves caused by the invagination of the nervous system have begun to disappear by 

 the growing togetiier of their edges, and instead of the deep furrows we tind a slightly depressed 

 line wliere the edges of the grooves have met (fig. 28, rg). 



In the nervous system a pair of tentacle nerves has been formed from each radial nerve (tig. 

 31, nl). They grow out laterally from the ladial nerves at ])oiuts proximal to the tirst pair of foot 

 tentacles, around which latter they grow and to which they belong. No nerves as yet have 

 appeared to supply the buccal tentacles. 



In "F" the buccal tentacles had only begun to curve away from the end of the arm; but iu 

 "<r" this proximal bendiug has continued until they curve over the nerve ring and point toward 

 the mouth. 



Beside this change in the water vascular system wo tind in "G" the first appearance of the 

 rudiments of the ])olian vesicles. They are four in immbcr and are in the form of small interra- 

 dial pou<;hes growing dislally fiom the convex wall of the water ring (tigs. 31 and 32, pv). There 

 is no polian vesicle present iu this species iu the stone canal iuterradius. 



