ACTINIARIA . 



5 



stinging threads. The nemathybomes are to be conceived as stinging batteries invaginated in the mesogloea. 

 Also the size of the scapus-nematocysts, in comparison with that of the nematocysts of the capitular ectoderm, 

 seems to depend on, whether the nematocysts are arranged in nemathybomes or not. In the genera provided 

 with nemathybomes, Edwardsia and Isoedwardsia, the nematocysts of the nemythybomes are narrow and long 

 and commonly several times as long as the small nematocysts of the capitulum. In the sub-family, Milne- 

 edwardsiinae, on the other hand, the nematocysts of the scapus are more short and broad and hardly larger 

 than the nematocysts of the capitular ectoderm, which are generally considerably larger here than in the 

 sub-family Edwardsiinae. Especially in Milne-edwardsia loveni and carnea there are numerous nematocysts 

 on the capitular ridges (textfigs. 75, 79). The ectoderm of the column probably never contains any spirocysts, 

 nor is it provided with longitudinal muscles ; sometimes there is a well-developed nerve-layer in the ectoderm 

 of the capitulum (in Edwardsia andresi and Paraedwardsia sarsii) . The mesogloea contains a few cells and are 

 more or less thickened; on the capitulum it forms the main part of the ridges, when any such appear (as 

 in Milne-edwardsia loveni and M. carnea). The endodermal, circular muscles are more or less developed, but 

 never concentrated to a sphincter ; they here and there break through the mesenteries, as always in the Acti- 

 niaria, and are thus in these places enclosed in the mesogloea. In Milne-edwardsia nathorstii and Paraedwardsia 

 sarsii nematocysts occur in the endoderm. 



The tentacles are short, in sexually ripe individuals probably never less than 12. As I have already 

 pointed out in a previous paper the tentacles are arranged in two different ways (compare Carlgren 1893; 

 1904). The first type, observed in different Edwardsia-species and in Isoedwardsia mediterranean, and 

 probably characteristic of these genera, we may call the Edwardsia-type (textfigs. 9, 10). It is characterized 

 by its inner tentacles, off-shoots from the endocoels, being shorter than the outer tentacles, an arrangement 

 which we find again in some Halcampoididae, viz. in Peachia, Eloactis and Haloclava. On the other side, in the 

 second type, the Milne-edwardsia-type (textfig. n) the inner tentacles are longer than the outer ones, as it 

 is commonly the case in the Actininae. Representatives of this type we meet in the genera Milne-edwardsia 

 and Paraedwardsia. This type is probably characteristic of these genera, as I have found such an arrange- 

 ment 1 in all cases where I have been able to undertake a thorough examination of them. The ectoderm of the 



1 Bourne (1916, Journ. Linn. Soc. 32 Zool. p. 513) has given an account of the order of succession of the micro-mesen- 

 teries and tentacles in the Edwardsiae. I think that in many respects his statements are erroneous. Edwardsia duodecimcirrata 

 (E. Liitkenii) is no Edwardsia but a Halcampa duodecimcirrata (compare Carlgren 1893 p. 38). The parasitic larva of Halcampa, 

 described by Haddon, is the larva of Peachia (Carlgren 1904. Zool. Anzeiger 27 p. 536). The arrangement of the tentacles and 

 the mesenteries in E. claparedii is that typical of the Edwardsia with 16 tentacles (compare the scheme and Carlgren 1904 1. c. 

 p. 543) and the grouping of the mesenteries evidently identical with that described by Bourne in E. beautempsii and willeyana. 

 (Andres has confounded the dorsal and the ventral side in E . claparedii ; in my paper (18933) I supposed that Andres's state- 

 ment of the tentacxJar arrangement was correct). Unfortunately the order of succession of the tentacles in the Edwardsia is not 

 known in details in any species, but we are obliged to construct it from different stages of different Edwardsia-species, a pro- 

 ceeding which always leads to a more or less uncertain result. In doing this we are in the first instance to study the tentacles 

 of live. specimens and, if necessary, to supply our observations with sections. As, however, the inner tentacles of ihe. genus Ed- 

 wardsia s. str. are (always?) shorter than the outer ones, as in Peachia, Eloactis and Haloclava, it is probable that the tentacles 

 9 12 are developed on a biradial plan (Carlgren 1904 1. c., a paper overlooked by Bourne), while in the genus Milne-edwardsia 

 the tentacles are arranged after the number 6 with the inner tentacles longer than the outer ones and the first 12 tentacles prob- 

 ably developing on a bilateral plan. (Carlgren 1893 textfig. 3, 4, 1893 b, textfig., 1904 p. 534). That the tentacles of E. clapa- 

 redii, A/, loveni and carnea are arranged in such a manner as here stated by me (textfigs. 9 n) is a fact that I have controlled 

 several times in living specimens and in sections. In living E. claparedii it is easily seen that the directive tentacles belong to 

 the inner, shorter tentacles which are often bending towards the mouth. The parts of the oral disc lying over the directive chamb- 



Thc Ingolf-Expedition. V. 9. 4 



