FISSION IN ACTINIA BERMUDENSIS VERRILL 47 



of the first and second ordeit vvith great accuracy. At the ends 

 of the siphonoglyphs (fig. 3) two directives coifld be made out 

 for each member of the most widely separated pair, while only 

 one directive extended from each of the members of the other 

 pair. A diamond-shaped area lying between the two mouths 

 was entirely destitute of mesenteries. In all, thirty-two complete 

 mesenteries were made out, of w^hich twenty-eight were arranged 

 in pairs, while four — two directives and two non-directives — - 

 were unpaired. Slight evidences of longitudinal infolding, es- 

 pecially at the oral end of the column, were apparent. 



Three w^eeks later the infolding (fig. 4) was very evident, and 

 the halves of the oral disc had almost completely separated. In 

 place of each of the two unpaired directives there was now a 

 paired directive, also in place of the two unpaired non-directives 

 there were paired non-directives. One of the halves of the ani- 

 mal (right) had formed another pair of complete mesenteries. 

 The opposite half had formed only a single complete non-direc- 

 tive, its mate being incomplete. During the next night rapid 

 fission had begun, and by morning had proceeded about 1 cm. 

 down the column. The fission continued rapidly and was com- 

 plete eight hours later, the whole of the final separation taking 

 from twelve to fourteen hours. The opposite walls of the 

 column had infolded until only a narrow strip of material joined 

 the halves. This narrow strip was ruptured by the straining 

 apart of the halves, the split moving in an aboral direction. 

 The ruptured surfaces w^ere immediately rolled inward, and the 

 animals contracted entirely, remaining in this state for five days. 

 Upon opening again, the wounds were seen to be completely 

 closed by a strip of salmon-pink tissue, 3 to 5 mm. wide, and 

 running the whole length of the column. The two animals were 

 then killed and dissected. 



Figure 5 shows cross-sections of both animals through the 

 region of the stomenteron. Daughter animal x (left in the figure) 

 had both pairs of directives developed; the w^hole left half, 

 which was that of the original specimen, was entirely normal, 

 having five pairs of complete and eighteen pairs of incomplete 

 mesenteries. The right half had formed three pairs, and one 



