558 ICHTHYOLOGY. 



(2) CYCLOIDS, (from Gr. kuklos, a circle,) those whose scales 

 are entire, as in the Salmon, Trout, Shiners, &c. 



(3) GANOIDS, (from Gr. gar^os, splendor.) having scales of 

 an angular form, composed of horny or bony substances, covered 

 with a thick coat of enamel, so that they become teeth-like in 

 their structure, as in the Gar-pike. 



(4) PLACOIDS, (from Gr. plax, a plate or slab.) thus named from 

 the irregularity which the scaly coverings exhibit, so that the skin 

 resembles shagreen as in the Sharks, Rays, &c. 



What is the fourth branch of Zoology ? Of what does it treat ? What is 

 said of the number of fishes? What are their most general characteristics? 

 What is said of their blood? Describe the breathing apparatus and the 

 circulation of the blood. What have they analogous to the lungs in 

 higher vertebrates? What purposes does it subserve? State its variation 

 in different fishes. Of what kind are the fishes which have not the air- 

 bladder? How does its possession expose to danger? What habit has the 

 Sea-Porcupine? What is related of the Gold-fish? What fishes sometimes 

 leave their proper element? Relate facts respecting the migration of Eels. 

 What is the usual form of fishes? What exceptions are mentioned? What 

 are the organs of motion? Of what do they consist? What orders are 

 based upon differences in their structure ? Of how many kinds are the 

 fins ? Name them, and describe their uses. What additional fin is men- 

 tioned? How do the bones compare in structure with those of other verte- 

 brates? What forms the skeleton of the Cartilaginous Fishes? What is 

 said of the vertebrae of fishes? What of the bones of the Herring and 

 Pilchard? What of the head? Describe the teeth, with their variations as 

 to form and number? What is said of the skin? What of its color- 

 ings? Of the senses of taste, smell, and hearing? Of their eyes? What 

 causes their brilliant hues? Where are the eyes placed ? Are these organs 

 wanting in any species of fish? What power is peculiar to some of this 

 class? Describe the electrical organs. Have they a voice? Do any give 

 forth sound? Describe their food. Are any fish viviparous? What are 

 the eggs in the mass called? What before exclusion? Where are they 

 deposited? What fish construct nests? Are any ovo-viviparous? What 

 singular facts are mentioned in regard to the male fishes ? What of the 

 Shark's eggs? Which is the most prolific fish? Give other instances from 

 the table. What facts show the longevity of fishes? What their capacity' to 

 endure heat and cold? Which species show the greatest tenacity of life? 

 What is said of their flesh? Explain the classification of Fishes as given 

 on the Chart. Which is the most anomalous of all the species? What 

 other strange fish are mentioned? Which connect the Fish and Reptiles? 

 Into how many orders are the Fishes arranged by Prince Bonaparte ? Give 

 their name, and also the orders of Agassiz and Muller ? 



Which of Agassiz' orders of fish figured on the Chart has a hetero-circal 

 or uneven tail or caudal fin ? How has this order been otherwise divided ? 

 Upon what are these divisions based ? Name the prominent fish in each. 

 Trace each family upon the Chart, giving some prominent characteristic of 

 each. Name some of the fish in each family, giving both the common, 



