PREFACE TO SECOND EDITION 



In the second edition of the Elasmohranch Fishes I have followed the same 

 plan as in the first, but I have added subject-matter and illustration which 

 should make this edition somewhat more complete. Especially is this true for 

 the chapter on the blood system to which has been added the work of Keys on 

 the liypobranchial arteries of Hexanchus. The findings on Hexanchus supple- 

 ment and add to my work on Hepfanchiis and make it more certain that the 

 blood supply to the pectoral area in primitive vertebrates was from tlie hypo- 

 branchial system, rather than from the dorsal aorta (the subclavians) as is 

 true for higher vertebrates. I have also included in this edition Professor 

 Van Wijhe's discovery that the thymus gland in the embryo of Heptanchus 

 cinereus is not ductless, and I have added experimental evidence to show that 

 the cutaneous vessels in Elasmobranchs are true blood-vessels. 



Berkeley, California, J. Frank Daniel 



February 24, 1928. 



PREFACE TO THIRD EDITION 



Among the contributions added to the third edition of Elasmobranch Fishes 

 is the work of Marine on the transformation of the endostyle of Ammocoetes 

 into the thyroid gland of the adult Cyclostome. Other contributions made 

 since the publication of the second edition are on the lymphatic system by 

 Hoyer, on the external carotid artery by O'Donoghue, and on the ampullae of 

 Lorenzini by Dotterweich. 



O'Donoghue has shown that the external carotid in Elasmobranchs, as in 

 higher types, belongs to the lower jaw, and that the artery in the orbit pre- 

 viously designated as the external carotid or posterior carotid is, in fact, com- 

 parable to the stapedial artery of mammals. Through this work we now have 

 a complete history of the externa] carotid artery from sharks to man. 



Dotterweich has shown that the wall of an ampulla of Lorenzini is made up 

 of two types of cells. One of these, a large goblet or gland cell, pours its secre- 

 tion into the ampulla; the other type is pj^ramidal and has an inside hex- 

 agonal face which is sensory in nature. An efferent nerve supplies the gland 

 cell, and an afferent nerve leaves each of the sensory cells. 



Berkeley, California, J. Frank Daniel 



January 4, 1934. 



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