THE ANATOMY OF ACTINIA MESEMBRYANTHEMUM. 221 



being more room for eggs on them owing to the absence of the 

 craspedum.* 



In Anthea the position of the fluted organ, and the features dis- 

 tinguishing it from the craspedum, are very obvious, as it is of a 

 brown hue, and throws up the white spots very clearly. I have not 

 examined Anthea very often, but my notes show the eggs in Novem- 

 ber growing, not on the sides, but on the edges of the septa in 

 bunches, and with tufts and sprays of craspedum intervening just as 

 in the case of S. parasitica. 



In S. troglodytes and all other Actinia? that I have met with, the 

 fluted organ is present. In all it is immediately distinguished if 

 viewed as an opaque object, but easily missed as a transparent one. 

 It is but slightly armed with capsules (cnidae of Grosse) whereas the 

 craspedum is fully armed with them. That it is a distinct organ, 

 and not a mere finish of the septum edge, I think is proved by its 

 position in T. crassicomis. In T. crassicornis, S. parasitica and 

 A. dianthus, it differs from A. mesembryanthemwn in having a keel- 

 like process or ridge all along the back (see Fig. 12, pi. XII). 



At first I hoped that it was connected with spermatozoa, but I 

 cannot confirm this view. The white spots on pressure were irre- 

 solvable, and under a power of 800 were only reducible to grape- 

 like bunches of small round grains, which, if it was not an optical 

 illusion, allowed a central beam of light to pass through them. 



It is an organ which makes its presence recognisable in the living 

 A. mesembryanthemum in a very distinct manner, for the disc will be 

 found on external examination to be marked with dots arranged in 

 two circles of 12 and 24 pairs, as in Fig. 18, pi. XII. The dots 

 in the inner circle will be seen with a lens to lie, not on, but under 

 the disc, and can be made out to be rows of the white spots of the 

 organ in question, and which appear just at the crowns of the 

 arches of the pairs of tertiary septa ; those attached to the secondary 

 septa do not show up through the disc, the depth of the arch of that 

 septum being too great to allow of it (see Fig. 14, pi. XII) ; but the 

 tertiary septa being shallow at the arch, bring the spots closer to 

 the disc. The outer row of spots is not alwa} s present in opaque 

 discs, but when it is present it is due to the same organ making its 

 appearance at the upper end of the edge of the quarternary septa 

 at the points where those septa blend off into the disc. 



* This distinction between the November and September aspects of the 

 parts shows the necessity of a continuous monthly series of observations. 



