88 Practical Zoology. 



which grow smaller by subdivision are arteries. The large tubes 

 which are formed by the union of smaller ones are the veins. The 

 finer tubes, forming a network in every direction, are the capil- 

 laries. They receive the blood from the arteries and pass it on to 

 the veins. 



Put on a higher power, a one-fifth or one-sixth objective. Study 

 the little bodies floating in the blood. These are the corpuscles. 



1. The colored corpuscles. The faintly colored elliptical cor- 

 puscles ; do they change their shape when pressed, as in turning a 

 corner ? What is the color of these corpuscles ? Mold a bit of 

 clay into the shape of one of these bodies. 



2. The colorless corpuscles. The smaller, rounder, paler cor- 

 puscles, fewer in number and moving with a slower and more un- 

 steady motion along the sides of the channel, what must be the 

 shape of these? Place a drop of frog's blood on a slide, cover 

 with a cover slip, and examine with a high power. Make careful 

 drawings of the two kinds of corpuscles. 



THE NERVOUS SYSTEM OF THE FROG. 



The nervous system is better seen in alcoholic specimens. Slit 

 the skin along the back from the snout to the anus ; with a sharp 

 knife cautiously cut away the top of the skull, and find : 



1. Between the eyes, side by side, two elongated white bodies, 

 the two halves, or hemispheres, of the cerebrum. Observe two 

 small, pear-shaped bodies, the olfactory lobes, in front of the cere- 

 bral hemispheres. These taper forward into nerves running to the 

 nasal region ; these are the nerves of smell, or olfactory nerves. 



2. Back of the cerebral hemispheres are the optic lobes, forming 

 the widest part of the brain. Prove that a white cord, the optic 

 nerve, connects each of these lobes with one of the eyes ; does 

 the optic nerve extend directly from each eye to the correspond- 

 ing optic lobe? Loosen and raise the brain from the front to 

 prove these points. 



3. Extending backward from the under side of the optic lobes 

 is the spinal bulb. 



