REPORT ON THE ECHINOIDEA. 13 



The genital plates and the ocular plates, as well as the madreporic body, make the 

 numerous combinations which have been so well traced by Lovdn, and which culminate 

 on the one side in such a compact apical system occupied mainly by the madreporic body, as 

 we have it in the Clypeastroicls, in which the genital openings in some cases no longer retain 

 a definite position in distinct plates, but may open anywhere in the interambulacral spaces ; 

 a state of things whose possibility is already foreshadowed in the genera belonging to 

 types early developed, such as Cidaris and the Echinothuridte. On the other side they 

 culminate in the great specialisation of the ocular and genital plates and their disturb- 

 ance by the interambulacral plates, encroaching between them, and little by httle 

 forming an excessive separation of the ambulacra into a bivium and a trivium, until little 

 by little it becomes again c^uite compact owing to the more equal development of the 

 coronal plates near the apical system. As Lov^n has well shown in the older Eehinids 

 {Cidaris and Salenia), we find all the proof we need of the crinoidial character of the 

 apical system of the Echinidse ; the calyx being more and more unimportant, though it 

 always reveals its typical features. 



In the Clypeastroids the calyx, though reduced again to its lowest limits, that is, 

 completely confused, still retains a few traces of its originally crinoid character, and in the 

 earliest appearance of the Spatangoid calyx we have introduced the embryonic element of 

 the structure of the calyx, which we find in late types of the present day, and which 

 recalls to us an arrangement of the plates of the calyx found in the Starfishes only. The 

 excessive splitting of the arms of an Ophiuran bring the abactinal madreporite to a 

 position adjoining the actinal opening. 



Fascicles. 



Fascioles as such are recognised only among the Spatangoids, but it is very probable 

 that such striking accumulations of miliaiy tubercles as we find on the edge of some of 

 the Phormosomas must be regarded as the first trace of fascioles, which we would thus be 

 led to consider as accumulations of miliary tubercles along certain lines, as we find them 

 in some genera of Spatangoids where their course is not well defined, until at last they 

 assume the fixity and clear definition which we consider so characteristic of our Spatan- 

 goids of the present clay. As far as my observations go they do not entirely agree with 

 those of Lovdn regarding the fixity of their position and the identity of their course in 

 older and younger specimens. Certainly, from what we have seen in the young of 

 Hemiaster cavernosus, both the course and position of the peripetalous fasciole is widely 

 different in the older and younger stages. In the one case the fasciole encloses the anal 

 system, in the other it is placed outside it. I have also shown the presence of such 

 rudimentary fascioles in Starfishes,^ so that fascioles are not confined to Eehinids. 



Alex. Agassiz, N. Am., Starfish, Cont. Nat. Hist. U. S., vol. v. 



