Vol. ;5J Torrcii. — Biological Studies on Corymorpha. 267 



they do not multiply so rapidly in the beginning; that when 

 they reach the number of four there is a pause in their develop- 

 ment, during Avhich the proximal tentacles continue to increase 

 in number without any delay; that by the time the proximal set 

 attains to little more than half its total number, the distal set 

 contains an equal number. From this point the distal set con- 

 tinues to increase more rapidly than the proximal, and ulti- 

 mately contains twice as many tentacles as the latter. 



The pause after the appearance of the fourth distal tentacle 

 seems to indicate that the development is according to a quar- 

 tette plan. Other facts suggest the same conclusion ; for in- 

 stance, the third and fourth tentacles appear almost invariably 

 in the same positions relatively to the other two, that is, in regu- 

 lar rotation. The numerical increase of the distal tentacles has 

 not been followed beyond this stage. 



There is nothing in the rhythm of the development of the 

 proximal tentacles to indicate quartettes. In serial diagrams 

 (5) and (6), however, the typical facts are represented that 

 Illpr. arises as far away as possible from Ipr. and Ilpr., while 

 IVpr. arises opposite Illpr. ; which suggest either a primitive 

 quartette formation that has been secondarily obscured, or a 

 dependence of the quartette arrangement upon mechanical 

 factors. 



The asymmetrical relation of the first two distal tentacles in 

 serial diagrams (4), (5) and (7) seems to find an explanation 

 in the assumption that they are slightly displaced in advance of 

 the appearance of 3d. With the appearance of 4d., they become 

 strictly opposite, as in (6). Each succeeding tentacle tends to 

 occupy a position in the widest available interval between any 

 two contiguous tentacles. This statement is well born out by the 

 proximal tentacles, a typical development being shown in (6). 

 IVpr. appears in the widest unoccupied space; Vpr. appears 

 without pause, as nearly opposite as possible, never contiguous, 

 in the next widest unoccupied space; VIpr. follows the same 

 rule. The tentacles may follow, in the order of their appear- 

 ance, the rotation of clock hands or the reverse. In either case, 

 the facts prompt the view that space considerations materially 

 assist in determining the type of tentacular development. 



