330 



Dr. C. F. Ltitken on Spontaneous 



groups of arms occurs in all possible degrees: the smaller 

 group may sometimes scarcely differ from the larger ; or it may 

 be reduced to 3 (1, 2) scarcely visible buds (fig. l,h). Of the 

 3 (or 4) regenerated arms the middle one (or 2) generally ap- 

 pears after the two outer ones. Numbers such as 4+2, or 



Fig. 1. 



Sketches of 9 individuals of Asterias problema, all represented of the 

 natural size. In most the madreporic plate is indicated. 



2 + 4, or 3 + 2, or 2 + 3 must be regarded as exceptions, as also 

 4 + 3 (fig. 1, b, c), or 3 + 4, or 4 + 4 (fig. 1, a), or 4 + 5, or 5 + 2, 

 in which the total number of arms exceeds six. Evidently in 

 all cases the smaller group of arms is developed long after the 

 other, and consequently there must have been a period when 

 all these starfishes had only 3 (or exceptionally 2, 4, or 5) 

 arms ; in examining a sufficient number of specimens we find 

 several with 3 arms, in which no trace of the deficient arms 

 can be discovered, and among these some (fig. l,g) in which the 

 place where the division probably took place, and where the 

 new arms will be formed, is still open. These specimens with 



3 arms (exceptionally with 2) I have found of all sizes, from 

 3 to 25 millims. or more in radius ; moreover, as the specimens 



