1880.] MR. F. J. BELL ON A NEW GENUS OF ECHINOIDS. 



45 



aphorism " The 'development of the individual is a compressed 

 epitome of the development of the race ;" and we may further look 

 for an explanation of the suddenness of the changes in the supposition 

 that between definite points in organization neither the larval form 

 nor the adult are enabled to maintain that equilibrium in the presence 

 of external forces which is necessary to the maintenance of existence'. 

 Whether this be so or not, neither the doctrine of Descent nor the 

 "fundamental principle of biogenetic development" has its truth in 

 any way affected thereby. 



It is with considerations of this kind in our mind that we must, 

 as I think, address ourselves to the consideration of intermediate 

 forms ; for, in our times at least, it is only when observation is kindled 

 by the light of the doctrine of the Descent that the full value of 

 " inoseulant forms" can be justly estimated. 



Description of the Specimen. 

 Amhulacral system. — The paired arrangement of the ambulacral 

 pores does not extend beyond the ambitus, which is very nearly 

 reached by all the five sets, hut most completely by the two postero- 

 lateral ; the two rows of each are, in the case of the postero-lateral 

 and of the anterior ambulacrum, altogether equal ; but in the antero- 

 lateral ambulacra the anterior row of pairs of pores is a little shorter 

 than the posterior, and this difference is best marked ou the left side ; 

 the strictest parallelism is observed between the paired rows, which 

 incline so slightly towards one another that the diminution in breadth 

 of the intraambulacral space cannot be detected by the eye until the 

 pores come close to the central or apical system ; here the pores 

 diminish considerably in size, but there is no bare space separating the 

 perforated ambulacral plates from the azygos radial plate, ordinarily 

 knovra as the ocular. The pores of the inner row in each pair are 

 still fairly circular ; those of the outer are more slit-like or comma- 

 shaped; and it is evident, so soon as several different pores have 

 been examined, that the specimen in question exhibits a commence- 

 ment of that union of the two pores by means of a connecting 

 furrow which is very much more, and quite distinctly, marked in 

 Echinolampas, and is even to be seen in Conoclypeus leskii, Goldfuss ". 

 The spacing-out of the ambulacral pores as they approach the 

 point at which the paired arrangement ceases to obtain is here but 

 barely marked ; and, indeed, it would be impossible to detect it at 

 all, were we not led to look for it from the marked degree which 

 it reaches in Echinolampas; so, again, while it is in some cases 

 possible to see that the terminal pores of the outer row of the 

 ambulacra are as completely circular as those of the inner row, 

 and so far to find an analogy with the much more marked simi- 

 larity in Echinolampas, yet in the cases of other rows on the same 



I The probability of sports leading to very considerable and remarkable changes 

 in organization has, comparatively lately, received support from the observations 

 of Mr. Bullar on the hermaphroditism of certain parasitic Isopoda (Journ. Anat. 

 & Phys. vol. xi. pp. 118-124). 



> ' Petrefacta Germaniue,' tab. xlii. figs. 1, a-c. 



