CTENOPHORA. 



23 



parent animal (— this can doubtless only take place through the enlargement of the size of the 

 embryo — ) it moves freely about in the usual way of Ctenophores — but probably only for a very 

 short time, as seems to be shown by the fact that the }'oungest fixed stage is scarcely larger (2""" 

 transverse diameter) than the Cydippid-enibryo still lying within the egg-membrane (1-5 "•">). The \-oung 

 Cydippid then attaches itself to the Untbclhila by the opened lobes; the secretion of the gland cells 

 found in the epidermis of the lobes may probably be of some use in the attachment. The ends of 

 the transverse furrow are now produced towards the aboral side (PL III, Fig. 3); at some distance 

 from the end, below the opening of the tentacle sheath, the two lobes unite with their edge, the 

 upper part of the furrow thus being separated from the larger under part. It is easily understood 

 how these separated-off lateral parts grow upwards carrying with them the tentacle sheath and thus 

 form the "chimneys" so characteristic of the grown animal. The upper ends of the furrow thus 

 become directly converted into the "chimney" openings. The change of their position from 

 vertical in the young to horizontal in the grown must be due to the part where the edges of the 

 lobes unite growing faster than the upper (adapical) side of the "chimney." 



The costse have already disappeared totally. Their role is only to carry the young 

 to a place some short distance away from the parent animal, they being thus reduced to be a temporary 

 means of dispersal. The very close packing of the combs, which must evidenth- check their loco- 

 motive power considerably, is in fair accordance with the reduction of their functionar\' importance. 



The gastrovascular system has undergone an important change from that found in the Cy- 

 dippid stage. As seen by the Fig. 3, PL III, the large entodermal sacs have begun to branch 

 at their outer end, which proves that they transform directly into the branching canals of the 

 grown animal. F'rom their base are seen to protrude a pair of smaller sacs. I do not doubt that 

 they will give rise to the genital vessels and the genital organs. The definite proof of this cannot 

 be given here, the specimen figured being unfortunately the onh' one found in the stage of meta- 

 morphosis from the Cydippid-larva to the grown form, and I have not thought it right to sacrifice 

 this highh' important specimen for section. The apical organ of this specimen could thus not be 

 studied more closely either, though it would have been ver\' interesting to see, whether it has alread\- 

 begun to degenerate at this stage. Another structure, the origin of which it would be highly interesting and 

 important to have made known, is the sense organ lying in the invagination above each genital organ in 

 the grown animal. The solution of these questions must be postponed till further material comes to hand. 



The question whether dissogony occurs or not mav be answered more definitely. It certainly 

 appears very improbable that dissogony takes place, seeing that the genital organs have not 

 yet begun to form in the C\dippid ready to leave the egg-membrane, and the free-swimming period 

 of the animal being probably only quite short, judging from the size of the youngest metamorphosed 

 specimen. Further, the observations of Chun (Dissogonie p. 102 — 103) have shown that the dis.so- 

 gony of Bolina and Eucharis takes place only under the influence of the high temperature of the 

 surface waters, not occurring during the winter season, and is not known either in the Ceslus larvse. 

 which during the summer months occur only in deep water, coming to the surface in the winter 

 months, and it would thus seem very improbable that dissogony should occur in Tfn/firlla, which lives 

 in the depths of the cold waters of Greenland. 



