ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 61 



added : — It lives on Synaptse in the English Channel and in the Adriatic. 



The animal, when extended, is from 0*25 to 0"15 mm. long. The 



2 

 ciliated oral funnel has a circular fold ; the formula for the jaws is -^, and 



the teeth diverge. The wall of the mid-gut is thick and of an intense 

 yellow colour, and the lumen of the gut makes therein a complicated 

 loop ; the mid-gut is attached to the dorsal wall by two bands. At the 

 anterior end there are two dorsal and one ventral gland (pancreas). 

 The hind-gut is formed of a pyriform vesicular portion, and a rectum. 

 Ciliated infundibula have been noticed in the neighbourhood of the 

 pharynx and brain. The gonads are germ-yolk-glands, which lie close 

 to the enteron ; a straight process passes backwards and downwards from 

 their investing membrane. The foot is three-jointed, and the penulti- 

 mate joint forms a sucker. A firm capsule is developed around the 

 isolated glandular ducts. The author believes that Echinoderes stands 

 nearer to the Kotatoria than to the Archiannelides. 



Echinodermata. 



Development of Calcareous Plates of Asterias.* — Mr. J. W. 

 Fewkes has investigated the development of the skeleton of some 

 American species of Asterias. He finds that the first plates to appear 

 are the terminals ; these are simple, and form a protecting cap which 

 shields the ambulacrals, interambulacrals and, possibly, marginals. The 

 genital plates arise after the terminals ; the one which lies nearest to the 

 madreporic opening does not always antedate in time or exceed in size 

 the other genitals ; the madreporite is not formed till after the rudiments 

 of the stone-canal. After the terminals and genitals there appears the 

 dorso-ventral, which arises before any plates are developed on the 

 actinal hemisome. The first set of body-plates are arranged in a circle, 

 and radially, inside the genitals ; the second is also radial and lies inside 

 the first or somatic radials. A third and inner circle appears before the 

 interradial somatic plate. The first plate in the circle outside that of 

 the genitals is the first dorsal of the arms ; this plate is the radial of 

 Sladen ; when the arm of the young star-fish is broken from the body it 

 always remains on the arm. The dorsals, or median row of plates on 

 the dorsal surface of the arm, originate peripherally to the first dorsal, 

 and are at first relatively very large. As the oldest dorso-laterals may 

 not be the nearest to the body, it is clear that they do not appear in the 

 same sequence as the dorsals. Marginal plates appear after the ambu- 

 lacrals (adambulacrals). 



The first plates to be developed on the actinal hemisome are the oral 

 ambulacrals ; at their first appearance there are already on the abactinal 

 hemisome five terminals, five genitals, one dorso-central, and thirty 

 spines on the terminals. The oral ambulacrals are at first set parallel 

 to the radial culs-de-sao of the water-system, but subsequently become 

 placed at right angles ; they are at first ten in number. The inter- 

 brachial ends of the oral ambulacrals of adjacent radii (arms) grow 

 towards each other, forming two parallel ends in each interradius, each 

 of which bears two spines. The median end of each oral ambulacral 

 bifurcates into a dorsal and a ventral part. All the other ambulacrals 

 arise with their axes at right angles to the line of the radii ; they are 



* Bull. Mus. Oomp. Zool, Cambridge, U.S.A., svii. (1888) pp. 1-56 (5 pis.). 



