A MONOGRAPH OF THE EXISTING CRINOIDS 11 



slight differences between the two arms of a pair has heretofore scarcely been discussed, 

 only occasionally illustrated, and possibly sometimes overlooked, because of its 

 transitory nature. Mortensen, indeed, denied it. When it is marked it seems to be 

 strongest in arms with from 10 to 15 brachials. 



Observations made by Gislen on very young individuals of Asterometra anthus and 

 Stenometra dentata point to the conclusion that one arm, usually the right arm, is 

 less favored in the earlier stages of development. It seemed possible to Gislen that in 

 reproductive arm regeneration the growth of one or the other arm might be more or 

 less favored, and that this might open up a possibility of drawing certain conclusions 

 regarding the tendency to suppression. In order to determine whether this could be 

 established for regenerates from the IB^ Gislen carried out experiments in regeneration 

 with Antedon petasus at the Kristineberg station. Owing to a number of unfortunate 

 accidents he obtained only 10 individuals with regenerated arms out of all the hundreds 

 operated upon. 



In 1918 he amputated the postradial series between the IBrj and IBr 2 in 15 

 individuals. The animals so treated were placed in a fairly large box with a lid 

 perforated with holes 10 mm. in diameter. The box was sunk off Blabergsbolmen, 

 Kristineberg, at a depth of about 15 meters and was anchored by a line to a crevice in 

 a rock just above high-water mark. When it was taken up a month later it was found 

 that all the individuals but one had escaped through the perforations. Fine-meshed 

 netting was then nailed over the perforations, and in 1919 the box was again placed 

 in position, this time with 50 amputated individuals. The strong September storms, 

 however, tore away the cable, and the box was lost. 



In 1922 the same procedure was repeated with a new box, but the circidation 

 within the box was too weak and the animals died. In 1923 he secured nine individuals 

 with regenerated arms. The regenerates obtained, however, did not give a final 

 solution to the problem, even though they furnished certain indications. The speci- 

 men obtained in 1918 had the anterior ray amputated. Of the two regenerated 

 arms the left was 1.5 mm. long, with 8 (9) brachials, and the right was 1.2 mm. long, 

 with 7 brachials. But an opposite result was shown by one of the nine regenerates 

 obtained in 1923. In this also the anterior postradial series is regenerated. The left 

 arm is distinctly the shorter, 1.4 mm. long, with 10 brachials, the right arm being 1.6 

 mm. long, with 11 brachials. No pinnules have developed. Four other individuals 

 show-ed either no difference or an almost imperceptible difference in the length of the 

 arms. The first of these, with the right posterior postradial series amputated, had 

 3 brachials on each side of the regenerated IBr axillary. The other three, two with the 

 anterior and one with the left anterior ray regenerated, had almost exactly equal arms 

 with from 15 to 20 brachials, supplied with from two to four pairs of minute pinnules 

 distally. About 12 proximal brachials lacked pinnules, as in the young, though 

 sometimes there were rudiments of Pi and P a . Of the four remaining regenerates 

 three had only three or four regenerated segments developed. In two of these the regen- 

 erated ray was the left anterior, and in one it was the anterior A minute ramification 

 consisting of a single segment appeared in one case to the right, and in one case to the 

 left. The last individual had regenerated in the left anterior radius an undivided arm 

 2.5 mm. long with the tip bent to the left consisting of about 11 segments. 



