February 17, 1!)05.] 



SCIENCE. 



265 



The niesoderni of ascidians comes from a 

 crescent of mesoplasm which surrounds the 

 posterior side of the egg just dorsal to the 

 equator. The substance of the crescent is 

 later infolded in the posterior and lateral 

 lips of the blastopore and its anterior por- 

 tion lies alongside of the notochord. There 

 are no mesoblastic teloblasts here, but with 

 this exception this condition closely re- 

 sembles Hatschek's account of the origin 

 of the mesoderm in Amphioxus. The 

 method of origin of the mesoderm in the 

 ascidians supports Rabl's theory that the 

 peristomal mesoderm is primary, the gas- 

 tral secondary, and that the latter is de- 

 rived from the former. 



The Skin, Lateral-Line Organs and Ear 

 as Organs of Equilibration: G. 11. Par- 

 ker, Harvard University. 

 Equilibration, as exemplified by the up- 

 right position of man, is in part carried 

 out through the eye, the ear, the sense of 

 touch and probably other senses such as 

 the muscle sense. It is a reflex involving 

 sense organs and muscular response ; hence 

 the term 'sense of equilibrium' is inappro- 

 priate. The lateral-line organs of fishes 

 have been supposed to be organs of equi- 

 libration. Lee has shown that when the 

 central end of the cut lateral-line nerve in 

 the dogfish is stimulated, compensating 

 movements occur in the fins ; but these 

 movements can also be called forth by stim- 

 ulating the skin in regions where no lateral- 

 line organs occur. Hence the skin is as 

 much an organ of equilibration as the 

 lateral-line organs. Both skin and lateral- 

 line organs are, however, inferior to the 

 eye and the ear as organs of equilibration. 

 The lateral-line organs are stimulated by 

 water vibrations of low rate, i. e., six per 

 second. 



The ear of the squeteague consists of a 

 utrieulus with three semicircular canals 

 and a saeculus containing a large otolith. 

 The cavities of the utrieulus and of the 



saeculus do not communicate with each 

 other. When the utrieulus and its semi- 

 circular canals are destroyed, the fish shows 

 equilibration disturbances, but no loss of 

 hearing. AVhen the otoliths of the sacculi 

 are made motionless by pinning them 

 against the lateral (non-nervous) walls of 

 the cavities in which they are, equilibrium 

 remains normal but hearing is for the most 

 part lost. In the fish ear the utrieulus is 

 the organ of equilibration, the saeculus 

 that of hearing. 



The skin, lateral-line organs and ears 

 represent, figuratively speaking, three gen- 

 erations of sense organs. The oldest is the 

 skin stimulated by varying pressures, such 

 as are produced by irregular currents, 

 and capable of initiating equilibration re- 

 sponses. From the skin have been derived 

 the lateral-line organs stimulated by water 

 vibrations of low rate, and also significant 

 for equilibration. Finally, from the lateral- 

 line organs have come the ears stimulated 

 by water vibrations of a high rate and im- 

 portant for equilibration. The ear, luilike 

 the skin and lateral-line organs, is differen- 

 tiated for its two functions, the saeculus 

 for hearing, the utrieulus for equilibra- 

 tion. 



Comparison of tJte Habits and Mode of 

 Life of Amphioxus and Ammocoetes : S. 



H. Gage, Cornell University. 



I. Both Amphioxus and Ammocostes live 

 in the sand completely covered. If the 

 head is projected or the entire animal re- 

 mains out in the water on top of the sand, 

 it is a sign of insufficient oxygen, too great 

 heat, or illness on the part of the animal. 



2. By repeated and contini;ous observa- 

 tion day and night I am led to believe that 

 when in good condition the two forms re- 

 main constantly under the sand day and 

 night ; they change their position in the 

 sand from time to time, however. 



3. In entering the sand from the water 

 there is a swimming motion until a consid- 



