668 HERRICK E. WILSON 



size in development (Fig. 10, No. 5). The lateral basals, with their 

 distal angles still in continuous growth-contact with the proximal 

 ends of the radials, would separate slightly and gradually at their 

 bases, as their longitudinal axes swung with the movement of the 

 radials. The posterior basal would also move outward from the 

 axial canal. These movements, however, are not migrational, but 

 are of approximately the same type found in normal growth (see 

 p. 502); for continuous growth along the plate margins, more 

 rapid in the expanding areas than elsewhere, would keep the plate 

 margins in continuous contact as in normal growth. 



Since expansion by proximo-lateral growth is obviously not as 

 rapid as by disto-lateral growth, the proximal ends of the basals 

 would probably not be carried out from the center of the cup by 

 growth pressure proportionately as far to the distal ends as they 

 are in normal growth. Thus the proximal ends would apparently 

 be lowered toward the horizontal plane of projection, and the pro- 

 jected angles of the proximal ends, which were 72 in the pentagonal 

 base, would approach 6o° in the hexagonal base. With greater 

 expansion in the sarcode and greater plate growth taking place in 

 the posterior region, the proximal angle of the enlarging posterior 

 basal would increase, while those of the lateral basals would 

 decrease through lengthening of their proximo-lateral margins by 

 growth as well as by change in the angle of projection and shifting 

 of their longitudinal axes. This method of basal change is sym- 

 metrical, normal, and apparently in keeping with the development 

 in Antedon and the early monocyclic and dicyclic Camerata as we 

 now know them. 



The first expression of the pent-up energy in the developing 

 intestine seems then to have been used up in a normal expansion 

 of the posterior interray, which in this group proved to be a plane 

 of weakness in the cup. Later, however, when the tendency for 

 spreading was established, this energy was expressed in another 

 direction, and in some of the modern crinoids (Pentometrocrinus, 

 etc.) results in an almost complete flattening of the dorsal cup. 



ii. The theory of the interpolation of a sixth basal factor to 

 the right of the posterior basal is based upon the appearance of 

 the radianal in that position in Sagenocrinus. It requires, first, the 



