ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 753 



The author next enters on an elaborate account of the structure 

 of the pedicels of the Echinoidea, into the details of which our space 

 prevents us following him. 



The next chapter deals with the important subject of the calycinal 

 system, which he defines as consisting of a central ossicle, five costals, 

 and five radials ; he urges with much point the value of using these 

 terms, and says truly that, when we know more " the final terminology 

 will come of itself." The differences between the Crinoid and the 

 Echinoid organization are sharply pointed out, and it is shown that 

 in the latter the system " is rendered, to no small extent, a disputed 

 ground, each of these (generative, water-vascular, anal) organs tend- 

 ing to penetrate its substance and gain access to the surrounding 

 water." Tiar echinus, with its enormoias calyx, appears to be the most 

 antique of Echinoids. While a number of forms retain a stable 

 relation of the parts we find that, when this is disturbed, the anal 

 orifice is the first to alter its position ; it is followed by the 

 madreporite and generative pores, but the eyes remain stationary. 

 The various stages of changes are traced in the most interesting and 

 instructive manner, and the whole history thus philosophically 

 summed up. " A large and powerful structure, closely specialized 

 for a function of fundamental importance in the economy of 

 some remote ancestral type, is inherited, in an early state, by a 

 descendant in which, from a total change in the mode of life, the very 

 purpose no longer exists for which it was originally contrived, and to 

 which its parts were adapted. It long retains certain marked features 

 which even to this day reveal its origin, but, unlike its crinoidean 

 sister-structure which, with functions unaltered, multiplies its com- 

 ponents — it remains simple as from the beginning, and, superfluous 

 as it has become, gradually declines in intrinsic vigour, and is given 

 up to subserving activities that had no share in its previous existence. 

 Invaded by contending organs and yielding to their various ten- 

 dencies it has its parts deeply modified and even to some degree 

 suppressed, and, although still true to its type, and asserting, so to 

 say, its unimpaired independence by redintegrating its injured frame, 

 it dwindles, nevertheless, from age to age in every succeeding form, 

 and is seen to fall into decay and dismemberment and to lose one by 

 one its characteristics, till at last little remains of its original 

 constitution. 



In trying to sum up the characters of the Pourtalesiadaa the 

 author feels the difficulty that the species which he has been able to 

 study most completely, P. jeffreysi is of a more advanced character 

 than the rest, but justly remarks that " this is not the first occasion, 

 nor will bo the last, when a species that chances to be the most 

 familiar to us is put forward as the typo of its kind." The general 

 form of the skeleton is subcylindroid, truncated anteriorly, tapering 

 posteriorly ; there is a deep infrafrontal recess and a rudimentary 

 buccal cavity. Bilateral symmetry is highly developed ; the peri- 

 somatic system predominates, while the calycinal is verging on decay. 

 'I'hc breach of continuity in two of the ambulacra is without parallel 

 among the members of the class. Like the Echinoneidfe they are 



