EMBRYOLOGY. PHYSIOLOGY. 
Ech. 17 
parts of the lower part of the body become replaced by a soft membrane, 
as the author has found to be the case in Agelacrinus and Hemicystites , by 
applying the method of thin sections. The author institutes a detailed 
comparison of the structure of his transitional Cystid genera with Aste- 
roids, and concludes that they might be grouped either with Asteroids or 
Cystids. The ancestor of Asteroids was sessile. 
IV. — EMBRYOLOGY. 
\ 
Semon (1) finds that the preoral band of starfish larvae is not pro- 
duced from the adoral band, as he formerly stated (Entwickelung der 
Synapta digitata ; see Zool. Rec. xxv, Echinoderms, p. 8) ; but is nipped 
off from a continuous postoral band, and its connection with the adoral 
band is secondary : hence the preoral area in Auricularia and Bipinnaria 
are homologous. All Echinoderm larva have a circumoral and an adoral 
band, of cilia. The Echinoderm Dipleurula cannot be compared with a 
Trochosphere ; its circumoral ciliated band is without a homologue in 
other larvae, and has been probably independently acquired. 
Although the Bipinnaria passes through an Auricularia stage, no trace 
of the nerve streaks of the latter were found, though they are probably 
present. 
V. — PHYSIOLOGY. 
Cu^ not (1) finds that the “ cellule mftriformes ” in the epidermis of 
Asterids secrete little vesicles, which appear to be venemous, and act as 
defensive organs. The dermal glands of Echinaster sepositus produce a 
similar secretion. The function of the vibratile radioles in Luidia and 
Astropecten is to direct currents of water to the lymphatic gills. The func- 
tion of the pedicillarise is purely defensive, to keep off parasites [ vide 
Biology, infra]. In feeding, nutritious substancos never enter the radial 
or stomachal coeca of starfish. The function of the anus is very limited, 
and waste matters are often ejected from the mouth. The granular cells 
of the digestive tract secrete an important digestive ferment. The 
stomach of a starfish is evaginated by compression of the ccelomic fluid, 
and drawn in again by the muscles of the mesenteries. In the nervous 
system of starfish, the radial cords serve each as the co-ordinating centres 
of their respective arms, while the oral ring acts as the co-ordinating 
centre for all the arms. The function of respiration is carried on by the 
hsemoxanthin of the blood corpuscles, acting similarly to haemoglobin. 
Excretory matters pass into the body cavity and escape by osmosis 
through the lymphatic gills ; there are no organs of excretion. The pro- 
ducts of digestion also pass into the body cavity by osmosis ; they are 
then probably taken up by the amoeboid corpuscles and stored up in a 
form similar to albumen, to be distributed to the tissues. The stone 
canal of Asterids has no current either inwards or outwards. It appears 
1890. [VOL. XXVII.] 0 2 
