302 PROPAGATION AND CLASSIFICATION OF ANNELIDA. 



dually detached by a narrowing of the preceding joint. Pre- 

 viously to its separation, however, the young one often forms 

 another bud from its own hinder part, in a similar manner; and 

 even three generations have been seen thus united. From observa- 

 tions recently made on another Marine Worm, in which a similar 

 occurrence takes place, it would appear that the buds thus 

 detached are, like the flowers of Plants, destined to Reproduc- 

 tion only; for whilst the parent continues to grow, to obtain its 

 food, and to develope new buds from its hinder portion, these 

 buds do not seem to grow into new individuals like their parents, 

 but, although possessing a head, mouth, and alimentary canal, 

 they do not take in nourishment, their functions being restricted 

 to the laying of eggs, from which new Nereids spring. Some- 

 thing analogous to this is met with among the Entozoa ; the 

 posterior segments, containing the ova, being detached from the 

 rest of the body, and thrown off altogether. 



837. This Class is subdivided into Orders, according to the 

 differences in general conformation and habits exhibited by the 

 tribes which compose it ; arid especially by the character and 

 distribution of the respiratory organs. The first Order, DORSI- 

 BRANCHIATA, includes those which have the branchial appendages 

 or gill-tufts disposed regularly along the body, sometimes extend- 

 ing along its entire length, and sometimes restricted to the 

 segments about the middle. This Order has been also denomi- 

 nated Errantia, from the active habits of the animals composing 

 it. II. In the next, TUBICOLA, we find worm-like animals 

 inhabiting fixed and permanent residences, like the testaceous 

 Mollusca. The disposition of the gill-tufts around the head, and 

 the absence of them along the body, is the principal character 

 which distinguishes the animals themselves from those of the first 

 Order. III. In the third Order, TERRICOLA, the body is desti- 

 tute of all external appendages, except some minute and almost 

 imperceptible bristles ; for the respiratory organs are here deve- 

 loped internally, the animal being usually formed to crawl upon 

 the ground, instead of swimming through the water. IV. And 

 in the last, SUCTORIA, the body is destitute even of these bristles, 

 but is furnished with a sucker at each extremity. 



