ZOOLOGY. 



Many undergo division without injury to themselves ; 

 yet the detached portions do not become again entire 

 animals. 



In most of them, however, the sexual parts of both 

 sexes are present, being associated with, though separate 

 and distinct from, each other ; those of the female mostly 

 opening upon the sides of the body. 



As being Dermatozoa, they have for the most part 

 special organs of sensation around the mouth, under the 

 form of papillae, filaments, spines and cups. The nervous 

 system, wherever it is to be met with, consists of a ring 

 surrounding the pharynx, and of a double ganglionic 

 cord lying along the ventral surface of the body. 



3244. Upon a higher stage of development the arte- 

 rial system gains the preponderance, and the blood 

 becomes mostly of a red colour Red-blooded Worms. 



3245. With the arterial the fibrous system also makes 

 a more decisive appearance. The tegument is a fibrous 

 tunic it is itself an artery. AH Annulate animals with 

 a fibrous tunic, which can consequently contract, belong 

 to this class, whether too they have red blood or not, 

 like the Holothurias and Star-fishes. 



3246. The Lumbricales or Earth-worms and the 

 Hirudines or Leeches respire obviously through the whole 

 tegument, though a special organ of respiration does 

 begin to be evolved, in the first family in the " saddle," in 

 the second in the lateral vesicles or cysts. 



3247. In others the branchial vessels make their 

 appearance above the level of the tegument as fila- 

 ments or ramules, and are arranged in two rows, as in 

 the common Sea- worm and in the Nereides. 



3248. Lastly, they accumulate aoout the neck or 

 head, as in the Amphitrites and Serpulariaa. 



3249. There are also Worms which respire only 

 through the intestine, its vascular system being bathed 

 on all sides by water, as in the Aphroditae. This water 

 becomes, as it would appear, simply imbibed by the 

 tegument in Thalassema, but through an opening at the 

 anal extremity of the body in the Holothuriae. 



