DEVELOPMENT OF ECHINODERMS. 45 



act of transfer. The effect of cystin on such eggs was indeed 

 most striking. Whereas in the controls hardly a pluteus was to 

 be found and these few were generally abnormal, the cystin eggs 

 nearly all formed normal plutei. The effect, also, of the cystin 

 on the development of the more normal eggs was perfectly in- 

 variable. The cystin eggs always showed a decided acceleration 

 of development, so that they were plutei while the controls were 

 still gastrulae. The acceleration was visible from about the fourth 

 division on. Plutei formed in the cystin solutions within 24 hours 

 of fertilization. The cystin not only accelerates the process of 

 pluteus formation, but a gradual acceleration of development 

 takes place from the start. 



We have, therefore, in cystin a substance which acts most bene- 

 ficially on Arbacia development, particularly in those cases where 

 the development is for some reason abnormal. It resembles in 

 this particular the action of alkalies as recorded by Loeb * and 

 pilocarpine in the case of star-fish eggs. 2 The conclusion is not 

 of course justified that the abnormality is due to a deficiency of 

 cystin possibly produced normally by intracellular digestion, al- 

 though such a possibility is not in itself improbable. If the eggs 

 are left in contact with cystin their death takes place after 48 

 hours, but if they are transferred to fresh sea-water after 24 hours 

 in the cystin water, theirsubsequent development does not appear 

 to be interfered with. They develop normally thereafter. 



Toward the star-fish eggs cystin proved to be toxic and the 

 only effect noticed was the early death of the egg. No accele- 

 ration was produced in the development of the mollusc, Cuiningia, 

 by the addition of cystin. The action appears, therefore, to be 

 rather specific for Arbacia. 



I also tried the action of tyrosin and an impure leucin from horn 

 upon Arbacia eggs. The tyrosin, while not very soluble, is more 

 soluble than cystin and accordingly more of it is in solution to 

 act on the eggs. A saturated solution was at first used, the sea- 

 water always containing undissolved tyrosin crystals. The effect 

 of such a saturated solution on the development of Arbacia, when 

 the experiments were tried in the same way as those with cystin, 

 was invariably harmful ; development was retarded and the eggs 



1 Loeb, Archi-v fur Entwickelungsmechanik, 1898, VII., p. 631. 



2 Mathews, Amer. Journal of Physiol., VI., 1901, p. 207. 



