No. 569] 



REGENERATION 



a homologous structure, the niadreporite and its stone 

 canal, occupies the dorsal interradial space. The num- 

 ber of vesicles varies in fact from one to four. By a 

 reference to Table I, it will be seen that out of 77 indi- 

 vidually examined, 41 had one, 20 had two, 14 had three, 



TABLE I 



To Show the Number of Polian Vesicles Present in a Given Number 



and 2 had four Polian bodies. If one is to test the matter 

 of regeneration, of course it is important to know 

 whether the variations or individual peculiarities will 

 be accurately reproduced. Another striking character- 

 istic comes out when we note in the same table the loca- 

 tion of these organs. Of the forty-one individuals which 

 had a single Polian vesicle, all were on the left side of 

 the animal, and 38 were in the left dorsal interradial 

 space. In twenty specimens with two Polian bodies each, 

 36 were on the left side and only four on the right side 

 of the body. A similar asymmetrical distribution of 

 these parts was found when three Polian bodies were 

 present. In one specimen, however, two vescicles were 

 found in one space, the left ventral interradius, the only 

 instance of this kind observed; on account of this dou- 

 bling, the right side lacked one of the number to which it 

 was entitled in the table. Where four Polian bodies are 

 present the arrangement is, of course, symmetrical on 

 both sides. Still another interesting fact comes out when 

 we examine the totals in the last line. Out of the 77 indi- 

 viduals, 71 had a Polian vesicle in the left dorsal inter- 

 radial space, 39 vesicles were found in the left ventral, 



