86 MR. A. D. DARBISHIRE ON THE DIRECTION OF THE 



On the Direction o£ the Aqueous Current in the Spiracle of the Dogfish ; 

 together with some Observations on the Respiratory Mechanism in other 

 Elasmobranch Fishes. By A. D. Darbishire, Demonstrator o£ Zoology 

 in the Royal College o£ Science, London. (Communicated by Professor 

 A. Dendy, D.Sc, Sec.L.S.) 



(With 3 Text-figures.) 



[Read 2nd May, 1907.] 



The observations which I have to record are the outcome of a suggestion made 

 to me by Prof. Dendy that 1 should find out whether water entered, or came 

 out of, the spiracle in the Dogfish. The point seems simple ; yet it is one 

 on which it is impossible to obtain definite information from text-books of 

 zoology. 



The observations were begun with Prof. Dendy, at the Royal College of 

 Science, on small Dogfish which had only just hatched; and were continued by 

 me at the Laboratory of the Marine Biological Association at Plymouth, where 

 I occupied the British Association Table. I wish to record my indebtedness 

 to the Staff' of the Laboratory at Plymouth for the trouble they took in 

 obtaining fish for me, and to Mr. A. I. Smith, in particular, for his help in 

 my observations. 



I shall first give an account of the general mechanism of respiration in 

 Scyllmm caidcula. This account is based on observations of more than twenty 

 Dogfish, which varied in length between 1 and 2 feet. The observations 

 were made partly in the large brick tank with a bottom of shingle and sand, 

 behind the Laboratory at Plymouth; and partly, when closer examination was 

 desired, in a glass vessel, to be described further on. 



The results obtained with the just-hatched Dogfish were not conclusive : I 

 shall therefore postpone reference to them until, after I have dealt with the 

 respiration as observed in the adult fish. 



SCYLLIUM. 



Each separate respiratory act in the Dogfish consists of an inspiratory and 

 of an expiratory phase. 



The term inspiratory phase may be given to the first phase of the act of 

 respiration, which commences when the whole branchial region begins to 

 expand and ends when this expansion has reached its full extent. Directly 

 this expansion begins (i) the mouth opens slightly, and (ii) the skin forming 

 the outer wall of each gill-slit becomes closely pressed against its corre- 

 sponding inner wall, evidently as a result of the incipient movement of water 

 towards it. This apposition of the two walls of each gill-slit continues until 

 the branchial region has reached its full state of expansion. The process of 



