308 EDW.^ED C. DAY 



seized with con\nilsions. The attacks, though violent, are 

 brief, and soon the animal is as erect and motionless as before. 



These sudden contractions at uTegular intervals are the only 

 vigorous muscular movements which the tunicate makes. They 

 are performed in order to clear the pharyngeal sac of foreign 

 particles, or to expel faeces, sperm, and mature ova from the 

 atrial chamber. When the animal is strongly stimulated around 

 either siphon, this characteristic vomiting reaction occurs. 

 Stamping on the sand or clapping two stones under water will call 

 forth a similar response. The lobes of either siphon are capable, 

 however, of individual response and react to feeble stimulation 

 with a local curling in of the lobe involved; a stronger stimulus 

 causes puckering of the other lobes as well, while a still more 

 vigorous application of the stimulus ehcits an almost simul- 

 taneous closure of both siphons, the one stimulated being usually 

 the first to respond. 



This response of the siphons being an easily observed reaction, 

 it served as a good indicator of the normal functioning of the 

 nervous system. The circlet of tentacles just inside the aperture 

 of the oral siphon which forms in some species a hairy strainer 

 to prevent too large bodies from being swept into the pharynx 

 with the ingoing current, could likewise be used as a reaction 

 indicator, though with less success. 



The lip-lobe reaction was bj^ far the most delicate of the two, 

 and through it the general kritabihty of the animal and the 

 conductivity of the ganghon could be studied under varied ex- 

 perimental conditions. Through this reaction the relation of 

 the central nervous system to the sense organs and musculature 

 could be fairly well ascertained, but as an index of the relation 

 of the ganglion to the activity of the visceral organs this reaction 

 was useless. 



While a few preliminarj^ studies were made upon Ascidia atra 

 Lesueur, a species found on the coral reefs of Bermuda, most of 

 the investigations were carried out on Ascidia mentula, Ciona 

 intestinalis, and Ascidia mammillata, but chiefly on Ascidia 

 mentula, at the Naples Zoological Station. 



