ACTINIARIA 



215 



As we see, in specimens 1-3 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 13, does not reach the actinopharynx here. The spec- 

 imen has only 15 perfect pairs. In specimen 4, which is provided 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 (x) had not " ' 

 arisen, the arrangement of 

 the perfect pairs of mesen- 

 teries would be the same as 



Fig. 202 A 



in the three first specimens. 



The following pairs 



of mesenteries consist of a 



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

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



mesentery. The letter indi- teries In figs ' 202 A and B only the sterUe 



mesentenes are reproduced. Compare the text! 



catesthe perfect mesentery. 



Sp. I. 

 Sp. 2. 

 Sp. 3. 



lob na i6b 



8a zob i6b 



lob i6b 



Fig. 202 C 



i8a 23b 243 26b 2Qb 303 = 10 pairs (202 B) 



i8a 23b 26b 3oa= 8 



i8a 243 3oa= 6 



Sp. 4. 4 b tob i?b 193 a6a =5 (202 A) 

 Sp. 5. 4 b lob 243 29b 313= 5 - (2026) 



The three first specimens as well as the greater part of 

 the specimen 5 fully agree. It is true that the same mesentery 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 n a in the specimen i is adequate to a stronger imper- 

 fect mesentery n 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 i6b, 19 a to i8a, 26 a to 243. 



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



