58 



the study of resorption or for the hydrogen-ion concentration 

 work, could not be carried out. 



Twice only I did obtain an animal feeding in its natural way. 

 They were both brought in with their prey. Once I got a 

 starfish, in the act of devouring a little snail, in its perivisceral fluid 

 aminoacids appeared by a positive ninhydrin-test to be present. 

 The other case was an Arbacia in the act of chewing up a 

 Clione sulfurea, a calcisponge. A ninhydrin-test again gave 

 positive results, no monoses could be demonstrated by means of 

 Fehling. 



Apart from these two cases I had to feed the animals artifi- 

 cially. Several substances were injected in that way for the 

 study of the resorption and in order to find out whether phago- 

 cytosis takes place in these forms. 



The injection of such liquids is very easy in the case of the 

 sea-urchins. If one lays an Arbacia on a table with the oral side up, 

 the lantern will start to perform rhythmical movements up and 

 down, accompanied by a circular movement of the distal part 

 of the lantern in a vertical plane. When the lantern is in its 

 most distal position, the teeth are closed tightly. When it moves 

 down again, i. e. towards the body, the jaws open up widely. 

 This is the moment to slip in the needle of an injection syringe. 

 With some practice one easily succeeds in bringing it down 

 just as far as the masticating apparatus reaches, without injuring 

 the tender gut behind it. The animal now tries to bite this 

 intruder, sometimes also brings it out of the centre of the five 

 teeth, pushing it down between two of them, so that it 

 leans against the circular „lip" and easily falls down. 



These movements resemble closely those described by Gem- 

 mill 43) and 44) in his papers on the locomotor function of the 

 lantern. He saw animals moving around by lurches on the 

 table — the same thing can also frequently be observed in our 

 Arbacia — and studied this method of locomotion a little more 

 in detail. The five little teeth, brought down in closed position, 

 form a powerful central stilt, which lifts the body. This body 

 of course capsises in a certain direction, which direction is 

 determined by the circular movements in a vertical plane, described 

 above. This method of locomotion seems to be rather common in 

 urchins ; not only Echinus esculentus. L. and Echinus miliaris. 

 Gmel., studied by Gemmill, show it, but also our Arbacia. 

 They move in that way in a rather surprisingly quick way; 

 in my work I was sometimes suddenly scared by one of the 

 animals dropping down from the table, from the centre of which 

 it had reached the rim. Even loaded — up to half a pound — 

 and on an inclined plane, they seem to be able to execute 

 these movements (Gemmill). In protruding the lantern, the 

 animal relaxes its posterior retractors and contracts the anterior 

 protractors. These same protractors serve to close the teeth. 



