Carbonate of Lime . . . 95'2965 . . 99.2922 Carbonate of Strontia . . . . 4'1043 Water 0'1544 . . 0'5992 it is composed of a considerable number of little plates, or faocttes (as in the fly), each of which receives a branch from the optic nerve. Such eyes are called Compound Eyes, whilst the Single Eyes, which exist sometimes in conjunction with the compound eyes in the same individual, are called Ocelli. The eye as an organ of sense is first distinctly developed in the Articulate Animals, as many of the organs which have been indicated as eyes In the Radiate Animals have probably no relation to the function of vision. Some anatomists have described organs of hearing in the Insects, whilst others regard the antennae as destined for the performance of this function.
The digestive apparatus of the A tticidata is for the most part in accorthuice with their carnivorous habits. Where animal flesh is eaten there digestion is a less complicated process than where vegetable food is principally partaken of. The mouth is generally provided with masticatory organs, which move laterally and are provided with palpi. Bard parts subservient also to the function of preparing the food for digestion, are also found in the intestinal cavity. The mucous membrane which covers the alimentary passages is of the simplest kind, whilst those glands which contribute to the digestive functions in the higher animals, as the salivary and pancreatic glands and the liver, are either not present or exist only in. the most elementary form.
The elongated form of the Articulate impresses this character on their circulating as well as digestive apparatus. In most of the articulate tribes the blood moves forwards in one or more large, dorsal, pulsating, arterial vessels. Side branches from these arteries are given off, and terminate in various trunks which convey the blood backwards to the dorsal vessel. The blood is more highly organised, has a deeper colour, containing a larger quantity of corpuscles and fibrin than in either the Radiate or Mulluscous classes.
The respiration is effected either by branchire, as in those which habitually live in water, sneh as the Crustacea, or by trochee, or airtubea formed of three parts, one membrane internal and one membrane external, both of which are cellular ; and a sort of cartilaginous elastic tube, rolled spirally, and placed between the two membranes. These trachea receive air by certain lateral openings
termed Stigmata. More rarely there exist cellular cavities analogous to lungs. In all instances the respiratory organs are perfectly symmetrical.
The following are the families of animals which are referred to the Articulate Type 1. Entoroa, including various forms of animals that inhabit the organs of higher animals. [Errozo.t.] 2. Rotifer a, or Wheel Animalcules, minute creatures scarcely visible to the naked eye, very abundant in all waters, and formerly classed with the Infusoria. [IforreERA.] 3. Annelida, or Annuloso Animals, including the Leeches, Worms, and Sea-Mice, mostly inhabiting water. [A.NxEmnAl 4. of which the Galley-Worm (Jules) and the Centipede may be taken as types, and which occupy an intermediate position between the highest and lowest forms of the class. [11YRIAll'ODA.] 5. Insecta, in which the locomotive power of the class is most fully developed, nearly all possessing wings for flight. [IesEcrAr] 6. Crustacea, the insects of the ocean, which breathe by gills instead of trachea, and include the well-known forms of Lobsters, Crabs, and Shrimps. fCRUSTACEd..] 7. Cirrhipedia, the Barnacles and Sea-Acorns. They were formerly referred to the Zilollusca, but their structure, habits, and economy place them amongst the Articulate. [CIRRIIIPEDIA.] 8. s rachnida, including Spiders, Scorpions, and Mites. They are distinguished from insects by possessing eight legs. Their instincts and intelligence place them at the head of this class as well as their structure. [ARActiNinA.] (Grant, Outlines of Compare tire Anatomy ; Owen, Lectures on Comparatire Anatomy ; Jones, Animal Kingdom; Cyclopedia of Anatomy and Physiology ; Carpenter, Principles of Physiology.)