CTENOPHORA. 



C. Regeneration. 



Several of the larger specimens of Tjalfiella in hand are remarkable through having the two 

 halves of the body unequally developed, the very different size of the two "chimneys" being especially 

 a conspicuous feature. The one chimney may be only half the size of the other, as in the specimen 

 represented in PI. I, Fig. 4, or even much smaller as in the specimen represented in PI. I, Fig. 8 --or 

 it may be totally wanting as seen in PI. I, Fig. 7. That the latter case is not due to damage done to the 

 specimen through capture is shown by the fact that the edges of the furrow have united below 

 the place of rupture. There can be no doubt that the figures quoted represent specimens in 

 different stages of regeneration. In the fig. 7 the regeneration has just begun, there being still no 

 trace of the organs lost, viz. the tentacle apparatus, the outer pair of genital organs and the whole 

 of the branching gastrovascular canals of that half of the body. In the specimen figured in PL I, 

 fig. 8, the regeneration has already been carried a considerable step farther. Both the tentacular 

 apparatus and the genital organs have been formed anew, though the tentacle itself appears not to 

 be developed as yet, and also the genital organs are still quite small. The branching gastrovascular 

 canal has also been formed, giving off already three main branches. In the specimen represented in 

 Fig. 4 the regeneration is nearly carried to the end; but the size of the whole right half and all its 

 organs as compared with the left sufficiently shows that also this specimen is in process of rege- 

 neration. (Also the fig. 9, PI. Ill, is from a specimen in regeneration). 



The histological processes of the regeneration have not been studied, the material in hand 

 being not sufficient for that purpose. That such a study will prove most interesting is beyond doubt. 

 Thus e. g. the formation of the genital organs and the sense organs attached to them might well be 

 studied in this way. 



The question arises here whether perhaps the animal divides itself by autotomy, the two 

 halves thus regenerating the part wanting. This question must evidently be answered in the negative. 

 If such were the case, the division would doubtless invariably take place along the middle line (the 

 sagittal plane), as appears to be really the case in the specimens represented in PL I, Figs. 4 and 8 

 - though the smaller size of the subsagittal genital organ of the not regenerating side makes it a 

 little uncertain whether the division line was really in the middle of the animal. But the specimen 

 represented in PL I, fig. 7 gives sufficient proof that no voluntary division has taken place here. The 

 division here has taken place between the subsagittal and subtransversal genital organs, only the 

 latter together with the tentacular apparatus and the "chimney" having been lost. It is evident that 

 a self-division along this line is not well imaginable. Specimens are also found in which the line of 

 fraction has been quite oblique; in one specimen there is only one large genital organ, all the other 

 being regenerated. There can thus be no doubt that the regeneration is caused not through 

 autotomy but by damage done to the animal, perhaps by fishes or Crustaceans feeding upon 

 it. The high percentage of specimens in regeneration among the material in hand shows that they 

 must be very exposed to such damage. 



The very great regenerative power thus shown to exist in this animal is the more interesting 

 as, according to Chun (Monograph, p. 241), the Ctenophores otherwise do not appear to be capable to 



