104 Animal Morphology. 



called sense apparatus, placed at the disposal of each special 

 sense, to enable it to accomplish that fixed purpose in the 

 animal economy for which the sense was destined, either for 

 protecting and preserving the being, or to make life more en- 

 joyable ; whilst the brain and spinal cord are membranes to 

 themselves, ruling and co-ordinating the several sense mem- 

 branes or sense apparatuses. 



Moreover, in the sense apparatus, membrane undergoes 

 an entire change in differentiation in its animal life. The order 

 of development is essentially segmental. To illustrate this 

 matter, let it be supposed that the typical vegetable mem- 

 brane shall be the intestinal canal from mouth to anus. We 

 have the serous and mucous membranes tolerably continuous, 

 and also the contractile membrane. The reverse of this 

 pertains to the sense apparatus of want, and also of force. 

 Take the former. The small intestines, liver, heart, and 

 lungs, as well as stomach, claim some share in the pneumo- 

 gastric, though, for reasons longer than can be here ex- 

 pressed, the liver and small bowels are provided to some 

 extent with nerves of force as well as of want, or the haemal 

 sense ; but accept its value as moderately correct, we have 

 the ch&st and abdomen under the guardian care of the 

 haamal sense. This sense has for its tripartite arrangement 

 three distinct membranes serous, mucous, and contrac- 

 tile. 



Of these, take the contractile membrane ; it includes all 

 the respiratory muscles as intercostal, abdominal, and 

 diaphragm, etc. Though all working in unison to one end 

 namely, to promote the function of respiration, and more 

 occasionally to empty abdominal fulness in the actions of 

 vomiting and defecation yet, in respect of attachment, as 

 of origin and insertion of muscles, though the end is empty- 

 ing out to make room for healthy material, with the ex- 

 ception of the diaphragm, every part of the contractile 



