778 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



From a study of successive stages of growing raedusEe the follow- 

 ing table is compiled to show the relation in time of appearance of 

 tentacles and sense-organs. The numbers in brackets in the column 

 of sense-organs indicate half-quartettes, the corresponding pair in 

 each case having been delayed in appearance. Since the sense- 

 organs are only half as numerous as the tentacles, they appear 

 with half the rapidity, and are therefore more frequently found in 



Tentacles. 

 2 



Larval 



Adult 



33 



Sense-Organs 

 .. (2) 

 .. 4 

 .. (6) 

 .. 8 

 ..(10) 

 .. 12 

 ..(14) 

 ..16 

 ,,(18) J 

 .. 20 

 ..(22) 

 .. 24 



this condition of incomplete quartettes. That is, if a Jelly-fish 

 were killed when the tentacles and sense-organs were in the 

 precise stage indicated by the line a h, for instance, the fifth 

 quartette of sense-organs would be found only half formed— five 

 sense-organs appearing in two opposite quadrants, and only four in 

 the other two. This is just the condition which exists in the speci- 

 men shown m PI. XXXII, fig. 19. The numbers indicating the 

 sense-organs are put at the intervals between those indicating ten- 

 tacles, to show that while the eight tentacles between the eight - 

 tentacled and the sixteen-tentacled stages, for instance, are appear- 

 ing, the four sense-organs which make up the second quadrant are 

 appearing. 



Another rule is followed by the marginal organs in their order of 



