50 INTRODUCTION. 



ferent degrees of organization. The simplest of all, the cestoid 

 species, the ligula, resemble a long striated ribbon, marked with 

 a longitudinal line. No external organ, not even suckers, are 

 perceived on them, and nothing internally, but oviform corpus- 

 cules in the mass of the body. Others again, whose forms are 

 much varied, such as the trematodes and tenioides, have only on 

 the exterior a greater or smaller number of suckers, sometimes 

 ramified in the body, which present other canals, either gem- 

 miferous or ovariferous. The acanthocephali echinorhynchi 

 have a proboscis armed with hooks, furnished with muscles; 

 they have two little coeca, and also either distinct oviducts, or 

 spermatic bladders, according to the sexes, which are sepa- 

 rated. The nematoides, as the ascarides, &c.; are still more 

 complexly organized; they have a mouth and anus, and an in- 

 testinal canal floating in a distinct abdominal cavity; their ex- 

 ternal skin is furnished with muscular fibres, in general, trans- 

 versely striated. They have distinct genital organs consisting 

 of long canals. The sexes are separated. They have a ner- 

 vous ring which surrounds the mouth, and two long cords, one 

 dorsal, the other ventral; they have also two spongy, lateral 

 vessels. 



40. The annelides or red blooded worms are vermiform 

 animals, whose elongated bodies are divided into numerous 

 rings, the first of which, called the head, differs but little from 

 the rest; the mouth is either a mere tube or jaws. There is an 

 intestine longer or shorter, which traverses the body; there is a 

 double system of arteries and veins, without any well defined 

 heart; the blood is red, the respiration branchial. They are 

 hermaphrodites, with a mutual copulation, they have muscles, 

 and the greater number, stiff bristles serving for feet; the head is 

 furnished with tentacula, and some of them with black points 

 that are considered as eyes; the nervous system consists in a 

 knotty cord. 



41. The other articulated animals, are all provided with 

 a head, and have all eyes, either simple or compound; their 

 very complex mouths, greatly resemble one another, and pre- 

 sent two modifications: in the first, for the purpose of grind- 

 ing, there are several pairs of lateral jaws, the anterior of which 



