96 



Fig. 18. 



ridoi Escn., it appeal's that tlie new chymiferous tubes are always 

 formed from the base of the digestive cavity towards the circular tube, 

 the tentacle which is eventually placed in the prolongation of the 

 chymiferous tube being always first developed, before any trace of the 

 chymiferous tubes can be found, so that the new chymiferous tube 



strikes the tentacle, instead of the 

 tentacle arising from the tube. Fig. 

 18 is a young Melicertum Campa- 

 nula Per. et Les., of which fig. 1 9 

 is the adult. In fig. 18 there are 

 only four of the eight chymiferous 

 tubes which reach the circular 

 tube ; the others, ^c, ^c, only ex- 

 tend a short distance, while the 

 tentacles 2, which will, in later 

 stages of growth, be found in the 

 prolongation of these tubes, ^c, are 

 The formula for the tentacles of fig. 18 



Young Melicertum Campanula. 



quite well developed. 



is: T;^, <3, ^25 i&i Tj, which soon becomes 



Tj, t^, <3, Tg, <3, ^4, Tj ; the chymiferous 



tubes 2c, ^c, having reached the circular tube 



at the point 2, fig. 18. The mathematical 



accuracy of the meeting of the tentacle and 



its chymiferous tube is still more striking in 



Willia. In a young Willia ornata McCr. 



there are four straight chymiferous tubes 



which do not branch, four long tentacles in 



the prolongation of these chymiferous tubes, Melicertum Campamila. 



and four tentacles which are not placed in the middle of the space 



between two adjoining chymiferous tubes, but always in such a 



position that, either to the right or the left, the distance to the 

 Fig. 20. nearest chymiferous tube is one-third of the space 



between two adjoining chymiferous tubes. In 

 fig. 20 the simple tube is sending off a small 

 branch, ^c, which will, in the end, strike the circu- 

 lar tube at the point where the tentacle 2 is 

 placed. The formula for the tentacles in fig. 

 20 being: T^, t^ T-^, and after the branch 

 of the chymiferous tube has reached the mar- 



for half 



gin it will become: Tg Tj, T^ x^^ 



the circumference: T-, indicatincj the tentacle 



Young Wilha ornata. . , '■ . ^ 



m the prolongation of the main tube; Tq the ten- 

 tacle of the first branch ; the ,-^-a,-^ joining the two letters T^ t^ 

 shows that the branch T2 is a part of the same chymiferous tube 



