NO. 19.] ECHINODERMS OF CONNECTICUT. 43 



MIGRATION 



It is well known that when the food supply in one region is 

 exhausted the starfishes migrate to other localities, and further- 

 more there is more or less regularly a seasonal migration from 

 the tide pools along the shore to the deeper water. But the 

 extent of such migrations has probably been greatly overesti- 

 mated, and the sudden appearance of vast hordes in any par- 

 ticular spot is due more to the very rapid increase in the size of 

 the small and previously unnoticed starfishes than to the actual 

 migration of a multitude of individuals. If a starfish should 

 move constantly in one direction at the rate of six inches per 

 minute, which is about its normal rate of progress, it could 

 travel about a mile per week ; but there is no evidence that such 

 a rate is maintained for more than a few minutes at a time, and 

 it is probable that the creature is quite as likely to retrace its 

 steps or to proceed in an irregular path as to continue for more 

 than a few minutes in any single direction. As stated in the 

 quotation on page 37, quicklime has proved an efficient barrier, 

 although the animals can easily pass all kinds of soft or slippery 

 substances. 



VARIATION IN NUMBER AND ARRANGEMENT 



OF RAYS 



- 



While all of our native species of starfish have normally 

 five rays of nearly equal size, yet if one examines a large number 

 of specimens he is likely to notice certain variations. In the 

 common starfish, for example, careful search may reveal an 

 individual with but a single well formed ray and other rudi- 

 mentary ones, while another specimen may have as many as 

 eight rays, all perfectly formed. 



EXPLANATION OF PLATE VII. Variation, Asterias forbesi. 



Fig. i. Four-armed individual, showing no indication of injury. 



Fig. 2. Eight-armed individual, provided with two madreporic plates. 



Fig. 3. An individual in which one arm is forked or longitudinally 



divided nearly to the disk. 

 Fig. 4. Six-armed specimen. 

 Fig. 5. One with seven well formed arms. 

 Fig. 6. An individual in which an injury has removed all the arms of 



the disk except one, the four small arms being in process of 



regeneration. 



(All figures two- thirds natural size.) 



