IO4 C. M. CHILD. 



disc is greater during the contracted condition than during dis- 

 tension, as in pieces with oblique discs. This fact indicates that 

 the muscles of the body-wall below the supplementary disc are 

 more completely relaxed during distension and orientation than 

 those of the opposite side (Child, '04^). The tissues gradually 

 adapt themselves to the altered conditions and the final result is 

 the form in which orientation in the typical manner is possible, 

 i. e., the typical or normal form. 



Supplementary Partial Discs Aboral to the (Esophagus. 



Loeb ('91) found it possible to produce the partial discs at any 

 level of the body except the extreme aboral region, but stated 

 that the tendency to closure of the cut without the formation of 

 a new disc is greater in the middle region than near the oral end. 

 Moreover, he found that the partial discs produced in the middle 

 region were without mouth-openings. 



My results agree with Loeb's in regard to these points, but, 

 since he did not turn his attention to the internal anatomy nor 

 investigate the nature of the distension, the reasons for these dif- 

 ferences did not become apparent to him. Apparently he was 

 not even aware that in making the lateral cut near the oral end 

 he was cutting into the cesophagus, while farther aborally only 

 the general enteric cavity was opened. I desire, therefore, to 

 point out certain very definite reasons why the results should 

 differ according to the position of the lateral cut in the cesopha- 

 geal region or aboral to it. 



There are several points to be considered, but the question as 

 to the effect of the lateral cut on the tentacles directly oral to it 

 naturally takes precedence as one of the immediate consequences 

 of the cut. 



According to Loeb, a lateral cut in the middle or aboral region 

 of the body does not cause any permanent difference between the 

 tentacles directly oral to it and the others ; here also my results 

 agree with his. His Figs. 2 and 3 show cases of this kind in 

 which the tentacles at the oral end are equal in length about the 

 whole circumference. 



If the collapse and reduction of tentacles be due to loss of in- 

 tracellular turgor in consequence of the cut there is no reason 



