208 



0. C. Glaser 



to activity and sluggishness is easy to see. An active individual 

 using four arms in progression has a much greater opportunity to 

 make "crosses" and "contacts" than if fewer arms w^ere used. 

 Very often v^hen the animals move by means of tw^o pairs of arms, 

 the anterior pair is crossed by the posterior regularly. The same 

 frequently happens when only three arms are used. 



Contacts and crosses also depend on the length of the arms, as 

 the chances that they will occur in long armed individuals are 

 greater than in short. How important arm length is, is indicated in 

 the following table in which are summarizedobservationson three 

 individuals which were active, but differed in the lengths of their 

 arms and also in the manner of using them. The effect of the 

 latter factor emphasizes that of the former. The longest armed 

 individual A used the "two pair of arms" stroke, only once in a 

 total of 141 effective backward strokes, whereas the shorter armed 

 individuals B and C, used this stroke eight times in 129 and four 

 times in 126, respectively. 



TABLE I 



RIGHTING MOVEMENTS 



Two types of righting movements were observed, only the first 

 of which has been described by von Uexkiill ('05) in an excellent 

 paper illustrated by means of kinetoscope photographs, and by 

 Grave ('00), who says: "Two adjacent arms straighten out so 

 that together they form a straight line. On these arms as an axis 

 the body revolves, being pushed over by the three remaining arms, 

 but mostly by the median one of the three. " 



This description, correct as far as it goes, is incomplete. At the 

 bases of the straightened arms, and in the interradial portion of 



