1912.] The Locomotor Function of the Lantern in Echinus. 103 



ciliation of the internal lining of the lantern coelom, of which the gill cavity 

 is a portion, and (2) the contractile nature of the gill wall. 



(1) If a single drop of methylene blue solution be injected by a needle 

 which just penetrates through the mouth membrane into the lantern coelom, 

 parts of the neighbouring gill will show some coloration after an interval 

 of a few- seconds. Here we have a means which in itself seems almost 

 sufficient for ordinary needs. 



(2) In Echinus esculentus the gill-walls possess contractility. Uexkull* 

 states definitely that in Sphcerechinus granulans the gill-walls are destitute 

 of muscular elements, and accordingly are entirely dependent for their 

 movements on the pressure within the lantern coelom. Obviously the 

 question is of very great importance as regards the mechanics of respiration. 

 In Echinus esculentus one may bring forward the following evidence for 

 contractility : — 



(a) Direct stimulation of a single gill, e.g. by touching with a needle, will 

 cause retraction of this gill without the others being affected. In very young 

 urchins, as Macbridef has shown, the lantern coelom is divided into five 

 separate compartments. However, in specimens measuring 2J inches and 

 upwards in equatorial shell diameter, I satisfied myself, by injecting 

 methylene blue with all due gentleness, that these compartments communicate 

 freely with one another. 



(b) Under a low power of the microscope in the undisturbed condition 

 individual terminal branches of any part of a gill may be seen occasionally 

 to contract or expand, apart from emptying or filling of the rest of the gill. 

 (This may be a local reflex depending on the condition as regards oxygen 

 and carbonic acid of the contained ccelomic fluid.) 



(c) Weak solutions of nicotine and certain other reagents will cause 

 active shrinkage of the gills. Nicotine is well known as possessing an 

 almost specific power of causing muscular tissue in urchins to contract 

 strongly. 



(d) Nitrite of amyl, on the other hand, has a relaxing action, and, if 

 carefully employed, may be used to remove moderate nicotine contractions. 



(e) The contractile property of the gill may be removed temporarily, but 

 completely, by exposure out of water. This method is referred to further on 

 p. 104. It is the best to employ in experiments regarding the influence of 

 internal pressure on turgescence of the gills. 



(/) Microscopic examination of sections of a gill shows just outside of the 



* "Uber die function der Poli'schen Blasen am Kauapparat d. regularen Seeigel," 

 ' Mitth. Zool. Station, Neapol.,' 1897, vol. 12, pp. 463—476, taf. 21. 



t "The Development of Echinus esculentus," 1 Phil. Trans.,' 1903, vol. 195, pp. 285—326. 



