!-!' ZOOLOGY. 



From this so called lachrymal irland, a few ducts proceed 

 ami penetrate through tin- conjunctiva towards the outer 

 aie^le of the eye; by the>e the ti-ars are conveyed to the 

 surface of the eyrl.all. Her.- they are spread over the Mirface 

 by the movements of the eyeball and eyelids, until they 

 collect towards the inner an^le of the eye, where will be 

 found the openings of two small ducts (puncta ladirvmalia) 

 ready tu convey away the superfluous tears. The fluid 

 entering these two short ducts is conveyed by them into the 

 lachrymal sac, which again communicates with the inferior 

 meat us of either nostril by the nasal duct. When thi> is 

 obstructed, the tears flow over the lower eyelid, constituting 

 the disease called fistula lachrymalis. 



Towards the inner angle of the eye is a small body, called 

 the caruncula lachrymalis; also a fold of the conjunctiva, 

 which is very small in man, being merely the vestige of a 

 structure which, in some other animals, as in birds, is carried 

 to its highest development. 



245. The structure of this apparatus is pretty nearly 

 the same in all mammals, birds, reptiles, and fishes. The eye 

 in certain mollusca also resembles the eye of animals much 

 higher in the range ; but in most of this class the structure 

 is very different, and as we descend to insects, cm- 

 arachnides, &c., the difference in structure becomes more and 

 more striking. These peculiarities will be adverted to here- 

 after. 



OF THE MOVEMENTS. 

 Muscular Contra rH<>,i. 



246. By sensation, man and animals perceive the ex- 

 ternal world ; by motion, they react upon it. This latter sei ie> 

 of functions is dependent on the property of contract '/ 'lit '>/. 



In some very simply organized animals, every part of the 

 body seems susceptible of con ti-acti n-- and elongating itself, 

 as in the hydra (Fig. 3) ; hut as we ascend in the ><-ale of 

 animals we find that the property belongs exclusively to the 

 ,,, a, .,)(] a,- Jil>r< . Collected in masses these form the ntn^i-J, \. 

 which again constitute the .//<*// of animals. Their colour, 

 which varies from a deep red to whitish, depends on the pre- 

 -ence of the blood, and is not inherent in their structure. 



247. Structure of (In .Mnxrlcs. The muscles are com- 

 posed of fasciculi, or bundles of fibres united by cellular tissue. 



