REPORT ON THE ACTINIARIA. 13 



troglodytes, because he mistook sections through the oral disk for sections through the 

 oesophagus. To avoid such errors it is only needful to bear in mind that the oral 

 disk has strong radial ectodermal or mesodermal muscles, whilst the CBSophagus is almost 

 always devoid of muscles on its ectodermal side. Oral disk and oesophagus can be also 

 easily distinguished by the different character of the epithelium. 



There are, however, numerous other difficulties attendant on the interpretation of 

 transverse sections, as the principles of arrangement are often not visible from the large 

 number of the septa which are pressed together and displaced by contraction. Such sec- 

 tions are, therefore, unadvisable in large forms, and especially in those of which we have 

 only a single specimen at our disposal ; in these cases dissection with knives and scissors is 

 preferable. For this purpose we find out the oral angle, and open the intraseptal space of 

 a pair of directive septa by an incision into the oesophagus ; when we have cut through 

 the base of the septum along the oesophagus, oral disk, wall and pedal disk, we have a 

 fixed starting-point, and are then able to detach the septa pair- by pair, and arrange them 

 in series one after another. Any one at all versed in the matter wiU soon know from the 

 size of the septa, from the distance of the directive septa, and from the way in which 

 the septa follow one another, when he lights upon the next pair of principal septa : he then 

 knows that he has examined one-sixth of the body, and does not require to investigate 

 the remaining five-sixths, as the same formation is repeated in the usual forms of Actinise. 



Another mode of preparation, which takes still less time, consists in detaching the 

 pedal disk in such a way that the bases of the septa still remain in it. By this means we 

 can easily see the arrangement of the septa, but not distinguish, however, how many of 

 them are complete. 



When we have separated and prepared the pairs of septa in the manner described, 

 we also get a view of the distribution of the tentacles which are evaginations both of 

 the intraseptal and the interseptal spaces. As a rule, each intraseptal space has only 

 a single tentacle, while the number borne by the interspaces may be greater. This is by 

 no means remarkable, as the interseptal spaces are seats of active growth. In those 

 Actiniae, in which there is a continual increase in the number of septa in the interspaces, 

 there is also a continuous evagination of new tentacles, and as the formation of the latter 

 precedes that of the former, it may happen that numerous tentacles are already present, 

 whilst the septa belonging to them are either entirely wanting or their rudiments only 

 perceptible. In Antholoha, for example, the innumerable tentacles of the umbrella 

 margin belong chiefly to the interspaces (PI. I. fig. 9). 



Like the septa the tentacles differ in age, so that we can distinguish tentacles of the 

 first, second, thii-d order, &c. This often causes distinction in size, which is best 

 seen in the CorallimorphidEe, where the entii-e arrangement of the septa is reflected 

 in the size of the tentacles (PI. II. figs. 1 and 3). The six largest tentacles belong 

 to the primary intraseptal spaces, the next six, which are only a little smaller, to the 



