CYCLOSTOMATA 



91 



15. The eggs are large and rich in yolk. It naturally follows that 

 the cleavage is meroblastic and the development is direct without 

 larval metamorphosis. 



It is probable that numbers 3, 4, 5, 6, 8, 10, 11, 13, and 14 represent 

 more primitive conditions than those found in the petromyzonts; 



mg 



be 



D 



FIG. 48. Bdellosloma. A. External view of whole animal, showing: be, bran- 

 chial clefts; mg, mucous glands. B. group of eggs adhering by anchor-like hooks. 

 C. ventral view of anterior end, showing somewhat ventral nostril, ventral mouth, 

 and oral tentacles; be, branchial clefts; x, resophageo-cutaneous duct. D. Larva, 

 showing functional eye. (Redrawn mainly after Dean.) 



while numbers 1, 2, 7, 9, 12, and 15 represent csenogenetic characters 

 resulting from specialization or degeneration. 



SUB-CLASS II. PETROMYZONTIA 



^ 



The lampreys live in both fresh and salt water, the marine species 

 being larger than those inhabiting streams. They live an active 

 predaceous life, attacking frequently fishes much larger than them- 

 selves, such as sharks. Their mode of attack is to give chase and to 

 attach themselves to the body of the prey by means of the sucker- 



