70 



DISCOPHOR^. 



Part III. 



Firj. 4. 



ENCOfE MiCBELlNl, Ag. A, B, C, D, E, the interambulacral zones. — I, II, III, IV, V, the am- 

 bulacral zones. — a, b and 1, 2, the respective halves of these systems. 



This being once understood, there can be no difficulty in homologizing the sys- 

 tems of radiating tubes of the Acalejjhs with those of the Echinoderms, as re^Dresented 

 from the abactinal surface in 

 Encope Michehni, Ficj. 4. Upon 

 removing the outer layer of 

 the solid envelope of this Sea- 

 urchin, there appear, in the 

 interambulacral zones, five sys- 

 tems of tubes (A, B, C, D, and 

 E), radiating towards the peri- 

 phery, and there anastomosing 

 with a circular marginal tube, 

 no mention of which has thus 

 far been made by any anato- 

 mist. These tubes are as nu- 

 merous and as complicated, and 

 anastomose as freely with one 

 another, as the radiating tubes 

 of any Acaleph; they occup}^, as in the Acalephs, the same structural zone as the 

 sexual organs, and are closely connected with them, as I shall show on another 



occasion. With these alternate the five 

 ambulacral zones (I, II, III, IV, and 

 V), the tubes of which anastomose, near 

 the periphery, with those of the inter- 

 ambulacral zones, as may be seen on 

 every point of the circumference, where 

 the tubes a and h of their respective 

 ambulacra I, II, III, IV, and V, unite 

 with the tubes I and 2 of their respect- 

 ive interambulacra A, B, C, D, and E. 

 And these two sets of tubes correspond 

 equally to the two sets already described 

 in Aurelia flavidula ; the ambulacral tubes 

 I a b, II h a, III a h, and IV b a of 



kmzuh 7^.K-m>m.k, Per. If U.S. I, II, III, IV, the amhula-ral zonej. — TT r ^^ i ,^ ^ ^ i 



A, B, CD, the interambulacral zones. -a, 6 and 1,2, 3. 4, the respective -'^ >9- '^5 COrreSpOnClmg tO the amOUlaCral 

 halves of these systems. , , _ , tt , -.-w^ ^.^.^ 



tubes I a b, II b a, III a b, IV a b, 

 and Y b a o? Encope Michelini, Fig. 4, and the interambulacral tubes A 1 2 3 4, 

 B 1 2 3 4, C 1 2 3 4, and B 1 2 3 4 of Fig. 5, corresponding to the interambu- 

 lacral tubes A 1 2, B 1 2, C 1 2, D 1 2, and E i 5 of Fig. 4 ; the only differ- 



