46 



condition and the significance of this in the philogeny. 

 HaeckeJ (ISSl), however, regards the appearance of two ten- 

 tacles in advance of the second two as an accidental and 

 insignificant occurrence, and takes four as the primary 

 niimber. '.Vhile this tendency to a paired origin of the ten- 

 tacles disappears after the earliest stages in Aurelia . 

 (jonionema exhibits this tendency in frequent instances dur- 

 ing the whole life of the animal. Its occurrence in the 

 appearance of the sense-organs is of the same significance, 

 because as will be pointed out below, these organs are mod- 

 ified tentacles. Figure 31 shows this condition in the 

 sense-organs, quadrants A and C having 5, while in quad- 

 rants B and D only 4 are yet developed. It is tirie that 

 other variations than these do occur in the appearance of 

 the tentacles and sense-organs of the adult, and in the 

 tentacles of the larva. Polyps with three, five or six 

 tentacles are not uncommon (Figs. 12. 24). It is notice- 

 able that departures from the normal number of tentacles 

 cori-espond very closely in polyps and adults. This would 

 be expected to be the case from the evidence that the lar- 

 val tentacles are permanent, and that they determine the 

 position of the four radial canals in the noi-mal medusae, 



