56 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The relations of the ossicles to the radial water-vessel and its 

 lateral branches are, further, of special importance ; this vessel lies, 

 from the first, ventrally to the rudimentary ossicles, and it is only 

 after some time that the branches to the feet become surrounded by 

 calcareous tissue ; in other words, the branches of the radial vessels 

 have at first the relation which they retain throughout life in the 

 Asteroidea. 



After some further consideration of these points, the author passes 

 to the terminal plate of the arm, as to which he has convinced himself 

 of the accuracy of J. Miiller's doctrine that this jDiece has primarily a 

 groove on its lower surface, and that it is only later on that it becomes 

 converted into a ring. The later observations of Prof. Ludwig have 

 convinced him of the accuracy of his comparison of the lateral plates 

 of the arm of an Ophiurid with the adambulacral jjieces of an arm of a 

 star-fish. 



The ventral plates are reported to commence as a small tri-radiate 

 body lying exactly in the middle line of the arm, with one aboral and 

 two adoral rays; these, then, notwithstanding opposing statements, 

 are unpaired pieces. The same is true of the dorsal plates. 



1'he interesting oral pieces of the skeleton are truly the modified 

 first ambulacral pieces ; a young Amphiura exhibits the possession of 

 nine skeletal pieces for each ray ; one of these is terminal and un- 

 paired, the other eight lie in four pairs symmetrically on either side 

 of a middle line ; of these two, more feebly developed, lie closer to 

 the median plane of the radius, and more deeply in the body ; the 

 other two are better developed, and lie more superficially ; the former 

 are the first two ambulacral, the other the first two adambulacral 

 pieces. The second pair of ambulacral pieces becomes more strongly 

 developed than the first pair, the two pieces of which, later on, form 

 thin calcareous plates, which descend further and further into the 

 angles of the mouth, remain se^^arated from one another, and, still 

 later, give rise to the two peristomial plates. The second pair unite 

 together and become connected with the first adambulacral pieces to 

 form the tori angulares. 



The first skeletal pieces to appear on the dorsal side are the five 

 terminal plates of the arms ; internally to them come the five primary 

 radials ; the central piece usually appears later on ; the intermediate 

 skeletal plates apj)ear around the central. The so-called radial shields 

 of the adult appear early at the outer edge of the radials. The author 

 points out the similarities in position between the primary madreporic 

 pore of Amphiura and the corresponding structure in the larva of 

 Antedon. 



Asterias.* — In the first part of his ' Contributions to the Systematic 

 Arrangement of the Asteroidea,' Prof. F. Jeffrey Bell discusses the 

 species of the genus Asterias; after giving a list of the 77 known 

 species, and of the 34 well-recognized synonyms, the author proceeds 

 to suggest an arrangement for breaking the species iip into groups ; 

 He first separates the sj^ecies " into those in which there are developed 



* Proc. Zool. Soc. Lond., 1881, pp. 492-515 (2 pis.). 



