EARLY -DEVELOPMENT OF GRIBRELLA OCVLATA. 399 



Relation of Larva to Adult. 



To anyone who has carefully followed the description of the various stages to F it 

 will be evident that there is a certain definite relation between the symmetry of the 

 larva and that of the adult. The sagittal plane of the larva, at least up to stage D, 

 i.e. as long as the larval entity can be recognised, is as nearly as possible at right angles 

 to the axis of symmetry of the adult, or, in other words, is parallel to the oral and 

 aboral planes or surfaces of the adult. Nothing is more clearly indicated in the processes 

 of growth than the fact that the left and right sides of the larva become respectively 

 the oral and aboral portions of the adult. In some of the transverse sections there is a 

 small angular deviation from this, but no more than can be accounted for partly by 

 distortion and partly by the knowledge that organisms can never be regulated by gonio- 

 meters. At later stages, from F onwards, or after fixation, it is quite true that the pre-oral 

 lobe of the larva becomes twisted somewhat upon the disc, usually in such a manner as 

 to bring the right lateral process backwards towards the right side (larval) or the aboral 

 side of the adult. At the same time, the disc is also twisted round in the same direction 

 to an even greater angle (fig. 90). The process can really be described as follows : — 

 the two lateral processes remain fixed to the foreign object, but the dorsal process, 

 and with it the whole disc, undergoes a twist through about 15° or so, in a counter- 

 clock-wise direction when viewed from above. I believe this to be purely a mechanical 

 torsion connected with the tendency of the disc to bend over to the oral side, which 

 increases till the whole disc touches the substratum and the attachment is lost. Many 

 of the advanced stages are entirely without this torsion, as in fig. 91, though in 

 this case the sucker can be seen adapting its shape to the ' pull ' of the disc over towards 

 the oral side. I have inquired very carefully into this point, as Goto has made some 

 somewhat startling statements concerning the relationships of larval and adult planes, 

 as discovered by him in Asterias pallida and in Asterina gibbosa. As will be seen 

 above, Cribrella does not lend any confirmation to his view. It is true that all pelagic 

 types of asterid larvae which I have examined usually have the disc in later stages at 

 the extreme posterior end of the larva, but the mere weight of the growing disc should 

 sufficiently account for this. Goto takes as a criterion of the larval planes the position 

 of the three brachiolar arms, and whenever these rotate in any direction, he assumes 

 that the larval planes have also been altered in position. This seems to me a falla- 

 cious method of determination, for the pre-oral lobe has different functions from the 

 rest of the body. If a ' sandwich-man ' parades the street with a board on his dorsal 

 and ventral surfaces, we do not regard these boards as lateral in position because he 

 turns his head to one side, but Goto's determination of the larval planes by the position 

 of the brachiolar arms appears to be based on much the same kind of deduction. 

 Goto's own figures of both species clearly show the same fact as those of many 

 previous workers, i.e., that the hydroccele and oral structures are moulded from the left 



