OF TREPANGS. 193 



tubular appendages to nothing but the tentacles which crown 

 the head progresses through a graduated series of changes, dur- 

 ing which the upper two, on the right and left, are obliterated 

 first. This is singularly exemplified in another of our native 

 Trepangs, which is pictured in this diagram (fig. 117) in profile. 

 Not only is it destitute of the two rows just mentioned, but the 

 median one of the remaining three is nearly obsolete ; thus leav- 

 ing the lower right and left (s) rows to perform the office to 

 which the Starfish devotes a fivefold number. But one step 

 more, and the reduction leaves no traces as in Caudina of 

 these appendages along the body. Coincidently with this pro- 

 cess the transverse filaments which go to these feet from the 

 nervous cords are also reduced, and thus the preponderance of 

 this system is thrown to the side opposite the heart, as these 

 figures (p. 122, figs. 57, 58) of the Zoophytic ideal type are in- 

 tended to express. 



This concentration of the nervous system, consequent upon 

 the reduction of parts from a higher to a lower number, is every- 

 where manifest throughout the animal kingdom, and nowhere so 

 conspicuously as among the jointed animals, the Articulata ; and 

 always coincidently with the elevation to successively higher 

 grades of being. It is, therefore, not to be overlooked among 

 the Zoophytes, although it is exhibited in so feeble a manner as 

 to almost escape detection unless upon the closest scrutiny.* 



The body is covered by closely set, semicircular, calcareous scales, a, a, the 

 branching tentacles ; a 1 , a 2 , the finer ramifications of a, waving to and fro in the 

 currents of water ; w, the web between the bases of the tentacles, forming with 

 the tentacles a deep, funnel-shaped vestibule to the mouth ; w, vermiform append- 

 ages, appearing like an outer circle of feelers ; an, the posterior opening of the 

 intestine ; s, the tubular appendages or suckers of the left, ventral row. Orig- 

 inal. 



* In order to anticipate the objection which no doubt wijl be raised by the ad- 

 vocates of the radiate type, I would remark, first, that I am not oblivious of the 

 apparent contradiction to this view in the process of the reduction of the ambu- 

 lacral rows of Echini ; and secondly, that it is only apparent, as may be ascer- 

 tained by a seriatim inspection of the various groups of the order. The whole 

 process culminates in producing a preponderance of the anlihcemal pair ; the so- 

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