1915 262 F. A. Bather — Studies in Edrioasteroidea. 



in that individual at least, the right side was higher than the left. 

 Let us, at any rate, test the hypothesis by applying it to the truly 

 remarkable disposition of the grooves in that specimen (text-fig. 1, c). 

 No sooner do we place the specimen on a slope, with the proximal region 

 of ray IV directed upwards, than all the hitherto inexplicable curves 

 appear the most obvious result of the downward pull. That peculiar 

 inward bend of ray IV is a simple downward sag where its course is 

 at right angles to the pull. The initial solar curves of rays III and 

 IV, and the initial contrasolar curve of ray Y, are similar sags, and 

 contrast with the greater straightness of the corresponding region in 

 rays I and II. Contrast again the sharp flexure of ray III, with the 

 more rounded curve of ray II, and the still more open curve of ray I. 

 At all points we see the action of the same force ; a force which may 

 be slight but which is always at work. Now at last we appreciate 

 the true meaning of what was previously styled the " peculiar aspect 

 of independent life " given to these rays by their varying curves. 

 There is here a struggle between two forces : the internal tendency 

 of the grooves to grow straight outwards from the mouth at equal 

 distances from one another, and the external pull of gravity, acting 

 equally on all the grooves, but affecting each in a different way 

 according to its position. Thus arises that unlikeness in likeness 

 which gives the fossil its peculiar beauty. 



If there be any truth in this explanation, it will of course be 

 necessary to suppose that other species, with rays otherwise disposed, 

 lived in a different position. In Agelacrinus hamiltotiensis, for 

 instance, ray IV must have lain more to the right, and so have come 

 under the pull of gravity on that side with the result that rays I, II, 

 III have a contrasolar bend, and rays IV and V a solar bend. In 

 that species, with no internal ampullae, groove Y has come right 

 round the anus. It is not quite so easy to explain those forms in 

 which all the grooves are either solar or contrasolar, but in the former 

 it is worth noting that ray V is not strongly bent in towards the anus 

 (see E. buchianus, 1900, Fl. VIII, and E. levts, 1914, PI. XII); it 

 would appear from this that the pull of gravity was, at any rate, not 

 being exerted in the same direction as in E. bigsbyi. The greater 

 width of interradius I-II in E. buchianus also suggests that its position 

 was uppermost, so that the anus lay to the left of the mouth instead 

 of to the right. In genera and species of later date, whether the 

 flexure be solar or contrasolar, we must not expect to find such direct 

 traces of mechanical causes. Those forms, we may most naturally 

 presume, repeat the direction impressed on their ancestors when the 

 conditions of life may have been different ; they themselves may 

 emphasize the direction by additional growth, as in the long lash-like 

 grooves of Dinocystis, but they are not likely to change it. 



Whatever truth there may be in the hypotheses here erected on the 

 suggestive fact of position first recorded by Dr. Foerste, it does at 

 least seem clear that all the differences may v very well be due to 

 simple mechanical causes acting on the growing animal. There is no 

 need to invoke any sudden change of structure or constitution, any 

 shuffling of chromosomes, or any reversal of development in early 

 stages, as, for instance, by the splitting of the fertilized ovum into 



