AGASSIZ AND WOOD WORTH : VARIATIONS IN EUCOPE. 129 



The youngest specimens of Eucope observed (eleven in number) had 

 twelve tentacles in all, one at the base of each of the four radial canals 

 and two in each quadrant with a sense organ, and without any tentacles 

 intermediate between the radial and the sense organ tentacle. It is 

 possible that these specimens may belong to a diflfereut species, as the 

 youngest specimens of Eucope diaphana I have raised from the hydroid 

 already had 24 tentacles.^ But of course it is possible that the above 

 stage may have dropped from the reproductive calycle at an earlier stage 

 of development. 



"Were the marginal tentacles to develop regularly we should have as 

 the third stage a Eucope with 48 tentacles, a fourth stage with 96, 

 and a fifth stage with 192. 



But as far as our experience shows, we find normal Eucope only in the 

 first and second stages, and even then there are numerous variations. 



The formulfe for the normal stages are, calling T any marginal 

 tentacle, 



Tj, the primary tentacle at the base of the radial canals ; 



To, the primary tentacle with a sense organ at its base ; 



ti, the first set of marginal tentacles appearing between T<, and T^ in 

 the stage with 24 marginal tentacles ; 



<2, the second set of marginal tentacles on each side of ti, in the stage 

 with 48 marginal tentacles ; 



ta, the third set of marginal tentacles on each side of (2, in the stage 

 with 96 marginal tentacles ; 



t^, the fourth set of marginal tentacles on each side of ts, in the stage 

 with 192 marginal tentacles; 



^5, the fifth set of marginal tentacles on each side of t^, in the next 

 stage with as many (theoretical number 31 tentacles) as 16^5, 8^4, 4/3, 

 2<2, 1^1 tentacles between the (T^ and Tq) radial canal and sense organ 

 tentacle, or 95 tentacles in each quadrant between the radial canals, or a 

 total theoretical number of 384 marginal tentacles. 



The formula of the youngest stage, or first stage, would be 

 2(4)T,+ (4)2To = 12T, 

 or two tentacles with a sense organ in each quadrant. 



That of the second stage, 



2 (4) T, + (4) 2 To + (4) 3t, = 24 T, 

 or two tentacles with a sense organ in each quadrant with a tentacle of 

 the ti order between each and the radial canal and sense organ, 



1 Proc. Boston Soc. Nat. Hist., June 4, 1862, p. 92. 



