ACTINIARIA 



we find also in other genera (compare above). In Polysiphonia there are, when 12 pairs of mesenteries have 

 regularly arisen, 12 development zones, in which the origin of new mesenteries takes place bilaterally from 

 both sides of the exocoels towards the centre of these latter. 



Some genera show a richer development of mesenteries in the distal than in the proximal part. This 

 is the case with Cymbactis, Synsicyonis and probably also with Antholoba (Archactis), in other genera the re- 

 versed takes place as in Stomphia, Pycnanthus, Parasicyonis, Sicyonis and probably also in Ophiodiscus. 1 Only 

 six pairs of perfect mesenteries are present in Actinoscyphia, Epiparactis, Paranthus! (sometimes), Anti- 

 paractis and "Paractis" ferax. In the genus Anthosactis we meet in ingolfi 6 pairs of perfect mesenteries, in 

 jan mayeni 8 and in excavata 12. In the other genera there are 12, or commonly more, perfect mesenteries. 



Also the distribution of the reproductive organs varies in the different genera. In the following 

 genera (and species) the reproductive organs begin to develop on the mesenteries of the first cycle. 



Ammophilactis , Anthosactis, Hormosoma, "Paractis" ferax, ignota, polaris, papaver , Paranthus, 

 Phelliopsis and Tealidium. 



The producing of reproductive organs begins on the second cycle in Actinoscyphia and Antiparactis, 

 on the third in Pycnanthus, Actinostola, Polysiphonia and Stomphia (partly), and on the fourth in Antholoba. 

 In the following genera, Ophiodiscus, Parasicyonis, Sicyonis and Synsicyonis, as a rule only the mesenteries 

 of the last order are fertile. In Parasicyonis these mesenteries are provided with filaments, in the other three 

 genera not. 



The longitudinal muscles of the mesenteries are, in comparison to the size of the animal, rather weak 

 and commonly form weak pennons or none. More developed they are for inst. in Hormosoma and Stomphia. 

 The best developed pennons we find in elongated forms, such as in Paranthus and "Paractis" ferax. The 

 parieto-basilar muscles are commonly well-developed, and so are also the basilar muscles. 



Genus Anthosactis Dan. 



Diagnosis: Paractiidae (Paractininae) with well developed basal disc, with smooth, rather low 

 body-wall, which is devoid of tubercles, acrorhagi and spirocysts, but more or less distinctly longitudinally 

 sulcated (in contracted state). Sphincter strong to very strong, not stratified, on transverse sections partite 

 in small meshes. Tentacles short, not particularly numerous, broad at the base, thinner at the apex, often 

 longitudinally sulcated, the inner longer than the outer ones or all of almost equal length. Outer cycles of 

 tentacles on the exterior side at the base with a well-developed stinging battery containing very large, parti- 

 cular nematocysts. Longitudinal muscles of the tentacles and radial muscles of the oral disc ectodermal to 

 meso-ectodermal, those on the inner side at the base considerably stronger than those on the outer side. 

 Oral disc very wide, in contracted state of the body strongly excavated. Actinopharynx short, with few 



1 It is true that Hertwig speaks of the presence of only 48 pairs of mesenteries and of almost 100 tentacles in Ophiodiscus 

 annulaius, but a closer examination of the figure 3 PI. to, encluding about one fourth of the oral disc, shows, that Hertwig has over- 

 estimated the number of tentacles so as to double the number. Probably this mistake is due to the bad preservation of the tentacles 

 or rather to an error in writing. If we namely consider the following suggestion by Hertwig, concerning the muscle-mesenteries (not 

 the with these latter alternating fertile mesenteries) in O.sulcatus (1882 p. 55): "Da im Ganzen 48 Tentakeln vorhanden sind, so wird 

 sich die Zahl der Muskelsepten gleichfalls auf 48 oder auf 24 Paare belaufen", we find, that the number of mesenteries in this species 

 is probably twice that of the tentacles. 



