44 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



Professor Verrill, of Yale University, has made a large col- 

 lection of these abnormal specimens, and has recently published* 

 a paper on the subject. On Plate VII are shown a number of 

 such specimens. Some of these are the result of injury, others 

 may have arisen from congenital variation, while others evidently 

 represent cases in which there has been a partial division of the 

 body in an early stage of development. Fig. 2, for example, 

 shows an individual which has eight perfectly formed rays, but 

 this specimen is also provided with two madreporic plates. 

 These facts would seem to indicate that in an early stage of de- 

 velopment, perhaps even at the time of the first cleavage of the 

 egg, the body became partially divided into two incomplete in- 

 dividuals. As development proceeded, these twins, as they may 

 be called, remained attached together, each provided with four 

 rays and the usual madreporic plate. A further and complete 

 separation might result either in two normal individuals, identi- 

 cal twins, or in such specimens as the one shown in Fig. I. On 

 the other hand it seems possible that the four-rayed starfish of 

 Fig. i may have resulted from an early injury and loss, without 

 regeneration, of the missing arm ; or as a so-called congenital vari- 

 ation, that is, one which has arisen very early in development, 

 but of which the cause is not apparent. In Fig. 3 is shown an 

 individual in which the arm opposite the madreporic plate is 

 forked or split longitudinally from the tip nearly to the disk. 

 This may be looked upon as a partial duplication or twinning 

 of this ray, or possibly as the result of early injury. 



Fig. 4 shows a variation in which there are six perfect rays, 

 while in Fig. 5 there are seven. The six-rayed condition is much 

 less rare than the other cases enumerated. From a great num- 

 ber of specimens which Professor Verrill has examined from near 

 New Haven, Connecticut, 1 in about 2,000 has six rays, 1 in 3,000 

 has four rays, and 1 in 10,000 has seven or eight rays.t Some 

 of these may be due to repairs of injuries received in early life, 

 with development of extra rays. 



The experimental studies of Dr. Helen D. King on the re- 

 generative processes in Asterias vulgaris t indicate the manner 



* American Naturalist, 1909. 



t hoc. cit., p. 546. 



t Archiv fiir Entivickelungsmechanik, vol. ix, 1900. 



