CHORDATA. 315 



5. The Eye. Remove the bone from above the eye and examine it in 

 position. How is the eye moved in life? Can you discover any of the 

 muscles effecting these motions ? How are they attached ? What is the 

 shape of the eye ? Split it open, and find the lens. Is the lens more or 

 less nearly spherical than you expected : . 



6. The Skeleton. The general shape and character of the skull and 

 its bones may be seen by boiling the head of another fish for a few minutes 

 and scraping and picking away the flesh. The principal regions are the 

 cranium or brain case, the opercular bones of the gill covers, and the 

 facial bones. Notice the loose way in which the lower jaw is articulated. 



Boil a two inch block taken from the tail of the fish for several 

 minutes. Notice incidentally the shape of the individual myotomes or 

 muscle segments as they fall apart. Clean the vertebrae of flesh, and study 

 the structure of one of them. Note the centrum; the dorsal or neural 

 arch and spine; the ventral or h&mal arch and spine. What is the shape 

 of. the centrum? What structures occupy the arches? Prepare a trunk 

 vertebra and 'compare in all respects with the caudal. How are the ribs 

 related to the vertebra? Can you find any evidence whether they are 

 homologous with the haemal processes? 



Are there any bones connected with the fins? 



D. General Questions. What internal organs show segmentation? Do 

 they show it equally in all parts of the body? Do the internal organs 

 show bilateral symmetry as completely as the external? How do you 

 account for the fact? Compare the relative position of the anterior and 

 posterior appendages in as many species of fish as you can secure? What 

 are the habits of the species you have been studying? Feeding habits; 

 spawning and breeding habits? What are its nearest relatives among the 

 fishes? 



334. The Frog (Rana). Any species of frog will serve. 

 For internal anatomy as large specimens as possible should be 

 used. The frog is especially suitable to represent the verte- 

 brates because of its metamorphosis from a water-breathing 

 or fish habit into the air-breathing condition, and the readiness 

 with which the main facts of this metamorphosis may be fol- 

 lowed even by an elementary class. Frogs may be kept alive 

 almost indefinitely, even through the winter, by putting them 

 in a deep box covered with netting, in which a pan of water 

 is placed. The bottom of the box should be covered by sod 

 or moss which must be kept moist. Change the water in the 

 pan every few days. Do not place large and small frogs in 

 the same box, as the small ones are more than likely to dis- 

 appear. Unless living animals, as grasshoppers and the like, 



