ZOOLOGY. 



within a cyst, has been found the Trichina spi- 

 ralis. This parasite has appeared most fre- 

 quently in Germany, and its presence is ascribed 

 to the use of pork, raw or imperfectly cooked, 

 in which the Trichina exists, for it also inhabits 

 the muscles of the hog as well as of the human 

 being. When thus encysted, it never develops 

 sexual organs, but must be again swallowed by 

 a warm-blooded vertebrate before it can repro- 

 duce itself. Its presence in the muscles gives rise 

 to the painful disease called Trichiniasis. The 

 non-parasitic forms are represented by the An- 

 guillulidce, which are little eel-like worms. One 

 species, A. tritici, causes the disease termed 

 'cockle' in wheat Another, A. aceti, is met with 

 in stale vinegar ; whilst a third, A. glutinis, or 

 * paste-eel/ is met with in paste that is turning sour. 



CLASS (C). Rotifera, or wheel-animalcules, re- 

 presented by such forms as Hydatina and Flos- 

 cularia, are microscopic aquatic animals, having 

 an elongated slightly segmented body, and carry- 

 ing at its anterior end a ciliated disc, which, by 

 creating a vortex, carries to their mouths any food 

 which may be floating in their neighbourhood. 

 They possess a mouth and intestinal canal ; and a 

 water-vascular system is present. They are very 

 tenacious of life ; so that, if they are dried until 

 they are quite brittle, on the return of moisture, 

 they unfold their wheel-like organs, and are as 

 active as before. 



troublesome to men and quadrupeds who have 

 occasion to walk, through the grass. They in- 

 sinuate themselves under the finest stockings, and 



CLASS (D). In the Annelida, the segmentation 

 of the body is generally distinctly recognisable, 

 and all the segments usually resemble each other, 

 except those at the two ends. If a segment carries 

 lateral appendages, these are never articulated to 

 the body. The digestive canal runs straight 

 through the animal from the mouth to the anus. 

 A system of canals exists, which contain a coloured 

 fluid, usually red or green, which is supposed to 

 represent the vascular system. The nervous sys- 

 tem consists of a double gangliated cord placed 

 ventrally, which encircles the gullet anteriorly. 



This class includes two sections : i. Abran- 

 fhiata, including the Leeches and Earth-worms, in 

 which there is no external respiratory organs or 

 branchiae. 2. Branchiata comprises the Tube- 

 worms (Tubicola) and the Sand- worms (Errantid), 

 in which branchiae are present. 



ORDER_I. Discophorahr example, the leeches, 

 which possess an adherent sucker at their an- 

 terior and posterior extremities, which they use 

 for locomotion. They have no lateral appendages. 

 The body has well-marked annulations. They are 

 aquatic, living chiefly in fresh water; but a few 

 are marine. The mouth of the Medicinal Leech 

 (Sanguisuga officinalis] is furnished with teeth 

 arranged in a tri-radiate manner. Each tooth has a 

 serrated edge, and when the teeth are worked back- 

 wards and forwards, they inflict the characteristic 

 leech-bite when these animals are applied to the 

 skin. Respiration is performed by the skin or by 

 involutions of the integument Leeches are her- 

 maphrodite, but they are incapable of self-impreg- 

 nation. They are very common in the south of 

 France, Bohemia, Hungary, and Russia. The 

 Horse-leech {Hcemopis sanguisorbd) is common 

 in Britain ; it is larger than the medicinal leech, 

 but its teeth are blunt, and it is useless for medical 

 purposes. In Ceylon, the Land-leech is very 



Horse-leech (Hcemopis sanguisorba), 



suck the blood of their victims ; so that the coffee- 

 planters are forced to wear Uech-gaiters of closelv 

 woven cloth for protection. 



ORDER 2. Oligochata comprise the Earth- 

 worms (Lumbricida:). Their organs of locomotion 

 consist of a double row of bristles attached to the 

 under surface of the body. They are all her- 

 maphrodite. The Common Earth-worm (Lumbri- 

 cus terrestris) is of great importance to the agri- 

 culturist, by continually bringing the deeper por- 

 tions of the soil to the surface. Besides they are 

 useful as food for birds and fishes, and their value 

 as bait is well known to every angler. 



ORDER 3. Tubicola are all marine, and they 

 invariably form for themselves a tube or case into 

 which they can retract themselves. This tube 

 maybe composed of particles of sand, which the 

 animal glues together with mucus, as in the genus 

 Terebella, or it may be of a horny, or even of a 

 calcareous nature, formed from matter excreted 

 by the animal. There is no organic connection 

 between the tube and its inhabitant, for the crea- 

 ture can be easily drawn out of it The organs of 

 respiration consist of a tuft of plume-like ciliated 

 organs situated on the head. These are often 

 beautifully coloured, from the coloured fluid, repre- 

 senting the blood, which circulates in them. The 

 genus Serpula, which forms irregularly twisted 



Serpula contortuplicata. 



calcareous tubes attached to shells and stones, is 

 very common along our coasts. 



ORDER 4. Errantia are free-swimming anne- 

 lids, which do not develop a tube. The seg- 

 mentation is distinctly pronounced, and the 

 anterior extremity of the body is marked out as 

 a head, which is usually provided with eyes. It 



