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the sea-urchins, (4) Holothuroidea—the sea-cucumbers, (5) Crinoidea 
—the sea-lillies and feather-stars. The common starfish was 
taken as a type, and its structure minutely described. It consists 
of a central disc and a number of arms or radii. The upper surface 
is studded with irregular nodules; here also is the vent and a 
little porous plate, the madreporite. In the centre of the under 
surface is the mouth ; along each ray is an ‘‘ ambulacral groove,” 
from which spring the “ tube-feet,’”’ by which the animal walks. 
These can be inflated at will by means of the complicated “‘ water 
vascular system’ connected with the madreporite. Above the 
mouth is a baggy stomach. The starfish, when feeding, protrudes 
its stomach through its mouth, enfolds with it its prey which it 
digests, and then withdraws it. Starfishes have generally—but 
not always—five arms. 
The Brittle-stars differ from the starfishes in having no ambu- 
lacral groove. In feeding they do not protrude the stomach, but 
pass the food into the mouth by means of the tube-feet. 
The Sea-urchins may be considered as starfishes whose upper 
surfaces have almost disappeared, the arms curled up to show the 
under side and coalesced, the nodules become spines amongst 
which are to be found the tube-feet. They live among rocks in 
which they make holes. 
The Sea-cucumbers are echinoderms in which the under surface 
is represented by the mouth end and the upper surface by the 
other extremity. The tube-feet are modified into branched 
tentacles round the mouth. Internally are vestiges of the ambu- 
lacral grooves. 
The Crinoides are now almost extinct. They grew on a jointed 
stalk. Their modern representatives, the feather-stars, break off 
from the stalk when mature and swim freely. 
Friday, April 20th. Sir Samuel Wilks, Bart., F.R.S., in the 
Chair. There was a good attendance of members. 
Mr. C, O, Bartrum, B.Sc., read a paper on ‘*‘ Some Present 
Views on Variation and Heredity.” He said that all 
animals and plants began existence as one single cell formed by 
the union of two cells from two parents. The nucleus determined 
the character of the offspring. Weismann, about twenty years 
ago, propounded a theory as to the “ mechanism” in the cell 
nucleus whereby the heritage is passed from parent to offspring, 
involving the principle of non-inheritance of acquired characters. 
This principle is now generally accepted. Galton has likened the 
main line of heredity to a chain-necklace and personalities to pen- 
