Prof. A. Schneider on the Actinia? and Corals. 437 



LIV. — On tlie Structure of the Actinice and Corals, 

 By Prof. A. Schneider*. 



[This is a report bj Prof, Schneider on the investigations 

 made by him and M. Rotteken in the Zoological Institute of 

 the University of Giessen. Prof. Schneider's own investiga- 

 tions relate solely to the laws of the position of the septa and 

 calcareous lamellae.] 



In the Hexactinia3 the septa always stand in pairs, as Hol- 

 lard has already correctly indicated, so that the members of 

 each pair are symmetrical in their formation. If we examine 

 a ti'ansverse section below the stomachal tube, we may distin- 

 guish three kinds of septa merely from the measure of their 

 radial diameter, which we may designate septa of the first, 

 second, and third order. The smallest number that occurred 

 consisted of six pairs of the first, six pairs of the second, and 

 twelve pairs of the third order. The six pairs of the first 

 order divide the circumference into six equal sectors, each of 

 which is again halved by a pair of the second order 5 the space 

 between a pair of the first and a pair of the second order is 

 then again halved by a pair of the third order. As Hollard 

 has already remarked, the septa bear upon the surfaces which 

 are turned towards each other very prominent, thick longitu- 

 dinal muscles, which we shall designate, for the sake of bre- 

 vity, by the name of vanes [Fahnen). In some Actiniae all 

 the septa bear vanes, in others only those of the first order. 

 But all the pairs by no means bear vanes on the surfaces 

 turned towards each other, as Hollard thinks ; there are al- 

 ways two diametrically opposite pairs of -p- ^ 

 the first order which bear the vanes on 

 the surfaces which are turned from each 

 other (fig. 1). Whatever number of septa 

 there may be in an Actinia (and their 

 number may be hundreds), there are al- 

 ways only septa of the three orders ; they 

 all stand in pairs ; and there are always 

 two pairs of septa distinguished as above 

 described, which indicate the bilateral symmetry of the Hex- 

 actiniae. 



Hitherto we have distinguished the septa of the three orders 

 only by the size ; but they are also distinguished by other pecu- 

 liarities of structure, as appears from M. Rotteken's accurate 

 investigations. 



In the Octactiniae the septa do not stand in pairs ; they also 



* Translated by W. S. Dallas, F.L.S., from the ' Sitzungsbericht der 

 Oberhessischen Gesellscliaft fur Natur- iind Heillninde,' March 8, 1871. 



