228 



LOWER INVERTEBRATES. 



when it retracts it closes its calcareous tube with an operculum. Over half a dozen 

 species are found on our northern coasts. The last form is Cistenides, or, as it is 



called in the older works, 

 Pectinaria. Our common 

 species, (J. gouldii, is light 

 red or flesh color, hand- 

 somely mottled with dark 

 red and blue. This species 

 forms long conical tubes of 

 sand, which are remarkable 

 in the fact that the grains 

 of which they are composed 

 are built up, a single layer 

 in thickness, "like minia- 

 ture masonry, and bound 

 together by a waterproof 

 cement." The animal is 

 shown in Fig. 217. 



Sub-Oedbk II. 



KANTIA. 



■ Er- 



Fio. 223. — Cirratulus grandis. 



The Errantia are active 

 and fierce beasts of prey, 

 of which the Nereidje .ind Nepthyd^ may be regarded as the central type. The para- 

 podia are large movable limbs, and bear numerous bristles varied in shape and color. 

 The tentacles on the head are often of several sorts, and the segments of the body may 

 vary in different regions, so that an anterior i)ortion of the body looks very different 

 from another posterior, as is so strikingly exemplified in Seteronereis and its allies ; the 

 segments of the bodies may also have gills of various kinds ; in some cases these gUls 

 are long and delicate filaments which entirely change the physiognomy of the worm. 



The term Nereis was given by Linnaeus to a group of annelids, which he charac- 

 terized as having an elongated veiTniform body, furnished with soft, well-developed 

 appendages, and a head bearing eyes and tentacles. He thus included nearly all the 

 Errantia under one genus, and the tradition of the Linnaean name still lingers in the 

 habit of naturalists, who use the term Nereis or Nereid as a vague designation. The 

 genus has now been very much reduced, by cutting off hundreds of its original mem- 

 bers to establish them under numerous new genera, so that the genus Nereis of to-day 

 is but a very small fragment of the original one. This has been the general fate of 

 all Linn6's names, so that while we have kept the form, we have rejected the sub- 

 stance, because the essence of his system of nomenclature was to give two names, one 

 to indicate the general place of the form in the animal kingdom, the other to desig- 

 nate the species ; but the modern genera, unlike the Linnsean, are no longer general 

 but special, and one of the chief merits of binomial nomenclature has been done away 

 with. 



Nereis pelagica is common on both sides of the North Atlantic, and is among the 

 longest and best known of vermes, but on the New England coast the much larger 

 Nereis virens is more readily found, for it lives in muddy and shelly sand between 



