70 C. M. Child 
proximal to the opening. Fig. 6 shows an individual with oral 
and aboral partial discs after the tentacles have attained complete 
development. 
These heteromorphic discs developed in every case—some 
twenty-five—where lateral incisions involving both _cesophagus 
and body-wall were made. 
Certain interesting modifications of the results occur when the 
lateral incisions are made in animals with the oral end more or 
less completely invaginated. These cases often occur against 
the will of the experimenter, for when the animals are first brought 
into the laboratory they are extremely sensitive and a very slight 
stimulus is sufficient to bring about 1 invagination. Consequently 
it often happens that more or less invagination has occurred before 
the scissors reach the cesophagus. ‘lwo cases will serve to indicate 
what may occur under these conditions. 
In the first of these cases the relation between the incision and 
the cesophagus and body-wall was approximately that indicated 
in Fig. 7. The cesophagus and disc had undergone a certain 
amount of invagination before the incision reached the cesophagus, 
consequently the portion of the cesophagus distal to the incision 
is shorter than the portion of the body-wall, as the figure shows. 
Union between cesophagus and body-wall above and below the 
incision occurred as usual in this case, but the regions of union 
occupy positions different from those in the preceding cases. 
Distal to the cut the body-wall and cesophagus unite at a, Fig. 8, 
i. €., at a point facing the lumen of the cesophagus when the animal 
is extended. Proximal to the incision the union occurs at 4, Fig. 
8. The results are exactly the same as if a lateral incision extend- 
ing obliquely toward the distal end of the body had been made 
while the animal was fully extended. ‘The new tentacles arise as 
usual in relation with, but a short distance from the line of union 
both above and below the incision. Consequently the tentacles 
below the incision, 1. e., the oral tentacles on the proximal portion, 
arise somewhat further proximally than in the preceding cases 
and the partial disc is somewhat oblique (compare Fig. 8 with 
Figs. 4and 5). In later stages this obliquity gradually disappears 
in consequence of growth of the body-wall proximal to these 
tentacles. 
