ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 631 



interradius in which is placed the remnant of the larval organ, and 

 is at the same time the anal interradius ; when the larval organ and 

 arms are both lost it may still be recognized by the fact that the 

 madreporite lies just to the left of it, in a dorsal view. 



Attention is next directed to the nervous system, which had 

 originally the form of an annular ridge encircling the point at which 

 the mouth is afterwards developed ; the epithelium above the radial 

 water-vessels thickens, and the radial nerves are developed from its 

 lower layers ; the rudiments are developed in an adoral and aboral 

 direction, but before they reach the tentacles they swell out to form 

 the eyes. 



Ludwig looks upon the ambulacral plates of Echinoids as being 

 homologous with the adambulacral plates of the Asterid and the 

 lateral plates of the arms of the Ophinrid ; the primary interradials 

 are homologous with the genital plates of Echinoids, and the five 

 pairs of plates which are found on the actual edge of the interradials 

 of the starfish correspond in position to the paired interambulacral 

 plates of Echinoids, and so represent a first pair of interambulacral 

 plates ; the so-called odontophore which the author previously took 

 to be an intermediate piece, is now regarded as an unpaired inter- 

 ambulacral plate. 



In conclusion attention is directed to the corm- theory of Echino- 

 derm structure which has been revived and pressed by Professor 

 Haeckel, the author considering that no support fur it is to be found 

 in the developmental history of any Echinoderm. 



Brisinga.* — Professor E. Perrier has some notes on this interest- 

 ing starfish, based on a study of sixteen well-preserved disks, two 

 young, and a large number of perfect, though single arms, in addition 

 to a magnificent specimen which was almost complete. Such a series 

 has, first of all, led him to the view that B. coronata and B. 

 endecacnemos are only two forms of the same species ; on the other 

 hand, a new form, B. edwarclsii has been dredged in the Atlantic ; in 

 this the arms are covered by imbricated plates, without spines. It is 

 pointed out that in Hymenodiscus the whole skeleton is reduced to the 

 ambulacral and adambulacral pieces, which, therefore, must alone be 

 regarded as the essential parts of an Asterid. In Brisinga we have 

 in addition, parts of the dorsal skeleton, which are arranged in arches, 

 more or less closely set ; these are, however, only found in the swollen 

 part of the arms, where the genital glands are developed, and they 

 are not to be seen in the young where the glands are still rudi- 

 mentary ; this set of plates must, therefore, throughout the whole 

 Asterid series, be looked on as an apparatus specially applied to the 

 purpose of protecting the reproductive glands. The disk of Brisinga 

 is formed early in life, around a digestive sac, the prolongations of 

 which are only developed later on ; these different facts appear to 

 support the doctrine the author has already taught, that the Echino- 

 derm, like the Medusa or the Coral, is the result of the fusion of 

 reproductive individuals around a central nutritive one. 



* Comptes Rendtts, xciv. (1882) pp. Gl-3. 



