ANNULATA. 279 



is also the reason why insects have no secretory glands, but are pro- 

 vided with mere spongy vessels, which, by the extent of their surface, 

 appear to absorb the peculiar juices they are to produce, from the 

 mass of the nutritive fluid. 



Insects vary infinitely as to the form of the organs of 'the mouth, 

 and those of digestion, as well as in their industry and mode of life. 



The Crustacea and Arachnides were long united with the Insecta 

 under one common name, and resemble them in many points of their 

 external form, in the disposition of their organs of motion, and of the 

 sensations, and even in those of manducation. 



CLASS I. 

 ANNULATA. 



THE Annulata are the only invertebrate animals that have red 

 blood. It circulates in a double system of complicated vessels. 



Their nervous system consists in a double knotted cord, like that 

 of insects. 



Their body is soft, more or less elongated, and divided frequently 

 into a considerable number of segments, or at least of transverse 

 plicae. 



They nearly all inhabit the water the Lumbrici or Earth-worms 

 excepted ; several penetrate into holes at the bottom, or construct 

 tubes there with the ooze or other matters, or even exude a calca- 

 reous substance, which envelopes them with a sort of tubular shell. 



Division of the Annulata into Three Orders. 



This class, which contains but few species, presents a sufficient 

 basis of division in its organs of respiration. 



The branchiae of some resemble tufts or arbusculae, attached to the 

 head or anterior part of the body : they nearly all inhabit tubes. We 

 will call them the TUBTCOLA. 



Those cf others resemble trees, tufts, laminae, or tubercles, in which 

 vessels ramify, and are placed on the middle of the body : most of them 

 inhabit mud or swim in the ocean, the smaller portion being furnished 

 with tubes. We name them the DORSIBRANCHIATA. 



Others again have no apparent branchiae, and respire, either by the 



