RESORPTION AND GROWTH IN THE CORONA. 229 



expect, that forms with scale-like imbricating plates are specialized not 

 primitive types.* 



Conclusions. 

 general res ul ts a nd their be a rijs' g. 



Under conclusions I would first consider the general results arrived at 

 in these studies and the bearings of the same. In the second part a new 

 classification is offered as the result of this investigation. In the preced- 

 ing pages the facts have been described and adhered to as closely as it 

 was in my power to do. Some conclusions are introduced, but only such 

 as seemed fully warranted and endorsed by the facts. In this chapter 

 on " General Results and their Bearing " I introduce some more theo- 

 retical conclusions which from their nature are not so capable of proof 

 and which I purposely avoided in the main bod}'' of the text. 



The late Professor Sven Loven, in his important work Echinologica (27)^ 

 says on page 17 : 



" In all the Echinoidea the growth of the corona is effected by new plates being 

 successively added at the aboral termination of the ambulacra and the interradia, 

 and by their increasing in size and soUdity. As long as the animal lives, there is at 

 work, more or less, in every part of its frame a continuous movement of reabsorp- 

 tion and renewal, of taking on one form and losing it for another, all in accordance 

 with the morphological canon of the species, and this process is perhaps nowhere 

 more conspicuous than in the corona of the Cidaridse and Echinidse." 



This statement, if accepted without careful consideration, might be 

 taken to mean that from the study of the corona of an adult we could 

 tell nothing as to what changes it had passed through and what was the 

 condition of the young, and this, as I think, I have proved would not be 

 true. To analyze Professor Loven's statement, all addition of plates to 

 the corona takes place dorsally close to the genital ring ; therefore the 

 plates at this area are the youngest plates and all other plates of the 

 corona are older in progressively increasing degree as we pass ventrally. 

 Plates increase in size and thickness because the plates of the test are 

 really internal structures and may receive additions by increment on the 

 proximal and distal aspects as well as on the sides of the plates. A good 

 example of this is seen in the initial plate 1' of the interambulacrum of 

 modern Echinarachnius or the Devonian Lepidechimts (plate 7, figure 42). 

 When first formed this plate must have been very tiny, but in an adult it 

 is relatively large, but still retains about the same angles of contour of this 



* Since the above was written Mr Charles Schuchert, of the National Museum, generously handed 

 over to me for inspection some very perfect specimens of Lepidechinus which Professor Beecher 

 had loaned him for stU'iy. This material corroborates what statements have been made, and alsa 

 shows many additional details of structure. 



