254 CASWELL GRAVE 



free-swimming period of the tadpole a contraction of each cup- 

 shaped enlargement takes place sufficient to extrude their viscid 

 contents upon the outer surface of the tunic and, when these 

 viscid droplets come into contact with the surface of some for- 

 eign body, the tadpole sticks fast. Attachment often takes 

 place shortly before metamorphic changes begin, and a tadpole 

 thus caught struggles actively to free itself, sometimes with 

 success, but more often without. 



When tadpoles are placed in Syracuse watch-glasses in quan- 

 tities of water sufficient only to cover the bottom, less than 50 

 per cent are likely to become attached, because under these 

 conditions the activities of the tadpoles do not bring the adhe- 

 sive papillae into contact with the glass surface of the dish, but, 

 if the quantity of water is sufficient to permit the tadpoles to 

 swim against the vertical side, attachment will take place in 

 practically all cases. Tadpoles which fail to attach to the side 

 or bottom of dishes well filled with water and remain floating 

 on the surface, are sometimes found to have small bubbles of air 

 adhering to them and, in these cases, the failure to swim or sink 

 below the surface is thus sufficiently explained, but many cases 

 of failure to become attached cannot be so simply accounted for. 

 The tadpoles which do not become attached, but remain floating, 

 are not abnormal, for they undergo metamorphosis as rapidly 

 and as normally and develop into ascidiozooids as normal as those 

 which become attached. 



In case the floating individuals happen to drift against the 

 surface of some foreign body, they may yet find attachment by 

 means of the new tunic material which is abundantly secreted 

 after metamorphosis begins. When first secreted it is somewhat 

 viscid, spreading over and adhering to the substratum. 



Initial attachment may be effected by the cement substance 

 exuded from any one of the adhesive papillae, and no indication 

 has been found that attachment takes place more often or more 

 effectively at one attachment point than at another. The point 

 by which attachment will be made apparently depends upon 

 which one first touches a foreign surface after the droplets of 

 cement substance have been extruded from the glandular ends 



