94 EECORD OF CURRENT RESEARCHES RELATING TO 



same direction ; in all cases it passes from left to right, save only in 

 tte Ophiurida. Tlie peculiar second coil in the Echinoidea is seen 

 to be the same in the Echinida and the Spatangida, if we place 

 representatives of these two groups in the positions which Professor 

 Loven regards as similar. 



(3) Bearing in mind the position of the stone-canal and the 

 direction of the enteric coil, we find that the bivium and trivium of 

 the Holothuroida are not comparable to the bivium and trivium of 

 the Spatangida. 



(4) In the Ophiurida the blood- vascular system presents the 

 same typical relations as in the Asterida or Echinoidea ; an aboral ring, 

 hitherto unobserved, is described as giving off" vessels to the genera- 

 tive organs, and as being connected by a cardiac plexus with the oral 

 ring ; this aboral ring is remarkable for lying partly under the 

 radial shields, and thence passing to the ventral side of the disk, 

 while another part passes to the genital glands, and, in fine, it has 

 the form of a ring provided with five central diverticula, which 

 pass towards the ventral side and come to lie just above the oral 

 shields ; this aboral ring in the Ophiurida is consequently homo- 

 logous with the dorsal ring of the Asterida and Echinoidea. 



(5) We now find that the oral shields of the Ophiurida are homo- 

 logous with the genital plates of the Echinoidea and Asterida, while 

 the oral plates of the Crinoida fall into the same category. From 

 these observations it would seem to follow that the homology which 

 Dr. Ludwig thought he had proved to exist between the first inter- 

 mediary skeletal plates of the Asterida and the oral shields of the 

 Ophiurida does not obtain, and that we are led, in addition, to see 

 that the circum-anal area of the Echinoidea corresponds to the whole 

 perisom of the Ophiurid disk, with the exception of the arms and oral 

 shields. 



Echinodermata of the Mediterranean.* — Dr. Hubert Ludwig 

 publishes a prodrome of a monograph of this group, in which he 

 gives a full bibliographical list of works on this subject, and a careful 

 account of the synonymy of the species. There are included alto- 

 gether 120, but of these 27 are more or less doubtful. Of the other 

 93, 2 belong to the Crinoida, 19 to the Asterida, 25 Ophiurida, 18 

 to the Echinoidea, and 29 to the Holothuroida. When we compare 

 this with the lists given by Sars (1857) or Heller (1868) we find a 

 considerable increase in point of numbers, for the former only men- 

 tioned 52, and the latter 75 species. It is of interest to note that the 

 opening of the Suez Canal has been of some influence in increasing 

 the variety of the Mediterranean fauna. 



Early Development of Echinids.t — Professor Emil Selenka has 

 studied, at Naples, the formation of the germ-layers and the origin of 

 the organs in Echinus miliaris, Toxopneustes brevispinosus, Strongylo- 

 centrotus lividus, Arbacia pustidosa, and Echinocardium cordatum. 



1. Yolk-division. — As in other Echinoderms cleavage is complete. 



* 'Mitth. Zool. Stat. Neapel,' i. (1879) p. 523. 

 t ' Zeitschr. wiss. Znol.,' xxxiii. (1879) p. ?.9. 



