250 THE AMERICAN MUSEUM JOURNAL 



bottom. One of these in section, discloses its curious occupant, the 

 strangest of all the worms. At first sight all resemblance to the other 

 worms seems to have become lost, and its entire structure is closely adapted 

 to its peculiar habitation which it never leaves. The appendages of the 

 middle segments of its body have united to form three circular "palettes" 

 which fit closely the interior of the tube and act like the pistons of a suction 

 pump, drawing the sea water in through one of the chimneys of the tube 

 to flow out at the other. This incoming stream bears the multitude of 

 minute organisms which form the food of the worm, and are abstracted 

 by a special apparatus as the water current passes over its body. Other 

 greatly modified worms are shown, such as the fringed worm {Cirratulus 

 grandis) with its threadlike breathing and prehensile organs, and the 

 trumpet worm (Pedinaria belgica) which builds a funnel-shaped tube of 

 sand-grains and digs rapidly in the sand with a pair of golden combs 

 borne upon its shoulders. 



All these are true worms which have become adapted in various ways 

 to their environment. The sandworm {Phascolosoma gouldii) however, 

 although externally wormlike, is internally of so different a structure that 

 it is doubtfully classed with the worms at all. Several are shown in the 

 group; some in a contracted condition, others expanded to disclose the slen- 

 der graceful neck and head wreathed with delicate flesh-tinted tentacles. 



In a second arbitrary cavity, are shown several of the so-called acorn 

 " worms" {Balanoglossus kowalevskii) — peculiar creatures with red " col- 

 lar" and tapering proboscis which they fill with water until rigid and utilize 

 as a digging organ. These "worms" swallow the mud for the sake of the 

 animal and vegetable matter contained in it, and after all nutriment is 

 extracted, cast it forth on the sea bottom at the entrance of their burrows 

 molded into little stringlike piles, many of which are represented in the 

 group. 



This acorn "worm" however has a far greater interest for science than 

 in its peculiar habits and adaptations. In spite of its wormlike body, it is 

 actually classed as an extremely primitive member of the same great group 

 to which we ourselves belong, the chordates, since it possesses certain 

 structures found only in that group. Its wormlike body, and probably 

 that of the sand worm, is a secondary adaptation to its burrowing mode of 

 life and illustrates the phenomenon of parallelism, the acquirement by 

 totally unrelated organisms of similar form or structure as the effect of a 

 similar environment. 



To sum up, the marine worms or any other group of animals in the midst 

 of their natural environment, may be considered as the members of an 

 interlocking and balanced association which is the net result and exemplifi- 

 cation of the laws underlying evolution. The great diversification of form 

 among the marine worms makes this especially clear, since diversification 

 means adaptation in the world of life. 



