7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 29 



pieces with oblique oral end the rapidity of tentacle regeneration differs on 

 different parts of the disc, being greatest on the uppermost (most oral) portion 

 and least on the lowest (most aboral) portion. These differences are probably 

 chiefly due to the local pressure exerted by the circulatory currents passing 

 orally in the intermesenterial chambers, which must be greater on the upper 

 side of the disc, where the angle between the disc and body-wall is acute, 

 than on the lower side where it is obtuse. The reduction in the obliquity of 

 the disc in oblique pieces is a compensatory process resulting from the attempt 

 of the animal to orient itself with its long axis vertical and disc horizontal; 

 unequal contraction of the muscles on different parts of the circumference occurs 

 and its continuation brings about changes in the tissues which lead gradually 

 toward the establishment of the typical form. In pieces cut wholly within the 

 stomodseal region the two cut ends of the stomodseum usually unite with the 

 cut ends of the body-wall, thus leaving the stomodseum open to the exterior at 

 both ends. Such pieces become slightly distended at first, but since the stomo- 

 dseum is not in communication with the coslenteron the internal pressure remains 

 far below that of the normal animal. Regeneration of the marginal tentacles 

 begins in such pieces, but never proceeds beyond the formation of mere buds. 

 Occasionally a stomodseal piece closes aborally by union of the body-wall across 

 the end of the stomodseum. In these cases communication between the stomo- 

 dseum and coelenteron is established, the piece becomes fully distended and 

 regeneration proceeds typically. The difference between the "closed" and 

 "open" stomodaeal pieces is due to the difference in degree of internal fluid 

 pressure. 



Child ( 5 ) finds that it is possible, by reduction of the internal water-pressure, 

 to cause reduction of fully grown normal tentacles in both G. solitarius and 

 membranaceus. The first stage in the reduction consists in a gradual decrease 

 in size of the tentacles, and in s. shrivelling and atrophy of the tentacles began 

 at their tips if the reduced pressure continued. In specimens which were kept 

 widely open the tentacles were reduced to small stumps. If specimens with 

 partially atrophied tentacles be allowed to close, the basal healthy portion of 

 the tentacle begins to extend as the internal pressure is re-established. Atrophy 

 of the distal portion of the tentacles occurs in specimens of s. which are kept 

 for a long time without food, and is also found in nearly all specimens taken 

 in mid-winter. Low temperature and starvation or exhaustion cause reduction 

 in the ciliary activity and therefore in internal pressure, and if such conditions 

 continue atrophy begins at the tips of the tentacles and proceeds proximally 

 as the reduction in pressure continues. See also Child ( 6 ). 



Davenport finds that longitudinal division is very common in Sagartia 

 lucicB and may take place in a few hours. Multiplication by basal fragmentation 

 is also probably common in nature. A piece without tentacles will produce a 

 normal individual with tentacles in 5 to 7 days. By longitudinal division the 

 12 stripes are apportioned to the 2 daughter individuals usually as follows - 

 8 + 4, 5 + 7 or 9 + 3. The condition of 0, 1 or 2 stripes is much less com- 

 mon and is the result of rapid and repeated division correlated with slow regene- 

 ration, at least of the stripes. The regenerated tissue is lighter in colour, the 

 old stripes are broader and of a deep orange colour, the new stripes are nar- 

 rower and at first of a lemon-yellow colour. The more vigorous the regeneration 

 the more numerous are the new stripes. These may appear early in the regene- 

 rated tissue and between each pair of mesenteries, or may appear later and 

 then tend to develop between the primary mesenteries only. The most common 

 condition is one with 12 stripes and 48 mesenteries. Division may occur before 



