CYCLOSTOMATA 223 



hunt at night. They are hermaphroditic, with an ovotestis, but one 

 sex always predominates. 



Petromyzontia. (Stone; suck in.) — The lampreys are found in 

 both fresh and salt water, the marine species being larger. They 

 are predaceous, true vertebrate parasites. (Brook lampreys are 

 not parasitic.) The lamprey breathes through the mouth except 

 when feeding, then through the gill clefts.^ Gage and Day of 

 Cornell University showed that the lake lampreys have in their 

 buccal glands an anticoagulating substance similar to " hirudin." 

 (See page 116.) 



The larvae, once called Ammocoetes, resemble Amphioxus. They 

 have a hood, median eye, endostyle, epibranchial groove (which 

 becomes the esophagus). The endostyle becomes the thyroid gland, 

 and the median fin specializes. 



1 Consult Gage, S. H. 1927. The Lampreys of New York State. Supp. to 

 17th. Ann. Report, N. Y. State Cons rvation Commission. 



Gage, S. H. 1929. Lampreys and tiieir ways. Sc. Mon., vol. 28, pp. 401-416, 

 May. 



Surface, H. A. 1897. Lampreys of Central New York. Bull. U. S, Fish. 

 Comm., vol. 18, pp. 210-215. 



Wheeler, W. M. 1900. Development of Urinogenital Organs of the Lamprey. 

 Zool. Jahrb., vol. 13, pp. 1-88. 



