ACTINIARIA 



215 



As we see, in specimens i — 3 the same pairs of mesenteries are perfect. In specimen 5 we find 

 mainly the same arrangement of the mesenteries. At the end of one half, the arrangement of the mesenteries is, 

 however, disturbed by an extra filament -bearing mesentery- 25 being intercalated. Besides, one of the 

 pairs of mesenteries, which are perfect in specimens i — 3, does not reach the actinopharynx here. The spec- 

 imen has only 15 perfect pairs. In specimen 4, wliicli is pro\-ided with 34 stronger pairs of mesenteries instead of 32 

 as in specimens i — 3, part 

 of the perfect pairs of mesen- 

 teries are of another number 

 than in the latter spec- 

 imens. If we imagine that 

 the also here developed ex- 

 tra-mesenteries (.r) had not 

 arisen, the arrangement of 

 the perfect pairs of mesen- 

 teries would be the same as 

 in the three first specimens. 



The following pairs 



of mesenteries consist of a 



Textfigs. 202 A, B,C. Sicyonis iuberculata. 



perfect and an imperfect Diagrams of the arrangement of the mesen- 



teries. In figs. 202 A and B only the sterile 

 mesenteries are reproduced. Compare the text ! 



Sp 

 Sp 

 Sp 



Sp 



23b 24a 26b 29b 30a = 10 pairs (202 B) 

 1 6b 1 8a 23b 26b 30a = 8 — 

 1 6b 1 8a 24a 30a = 6 — 



17b 19a 26a ^5 — (202 A) " 

 24a 29b 31a = 5 — (202 C) 



mesentery. The letter indi- 

 cates the perfect mesentery . 



Sp. I. 4b lob iia i6b 18a 

 4b 8a lob 

 4b lob 

 4b lob 

 4b lob 



The three iirst specimens as well as the greater part of 

 the specimen 5 fully agree. It is true that the same mesenter>' is 

 not always perfect, owing to the different number of the pairs, consist- 

 ing of an imperfect and a perfect mesentery which are present in the 

 five specimens, but it is the same a and b mesenteries which are per- 

 fect in the pairs. Now one pair, now another thus seems to grow more rapidly. Besides, it ought to be 

 observed that also several pairs of imperfect mesenteries show a different development of both mesenteries 

 in one and the same pair. So the perfect mesentery 8 a in the specimen 2 corresponds to a stronger imperfect 

 mesentery 8 a in the specimen i.The perfect mesentery 11 a in the specimen i is adequate to a stronger imper- 

 fect mesentery 11 a in the specimen 2, and this is also the case with the mesentery 24 a. If we disregard the 

 presence of the extra pairs of mesenteries x (compare above) in the specimen 4, the arrangement of the me- 

 senteries is also here the same, 17 b corresponds to 16 b, 19 a to 18 a, 26 a to 24 a. 



How this peculiar arrangement has arisen, is difficult to decide. As to the place of the mesenteries 



Fig. 202 C 



