CERIANTIIARIA. 



The length and structure of the different mesenteries vary considerably in Ceriantharia. The 

 directive mesenteries are always sterile and as a rule without special differentiation of the filaments 

 (see p. 50), the remaining mesenteries may be distinguished as fertile and sterile in regular alter- 

 nation. A division into mesenteries bearing filaments and mesenteries bearing sexual organs, such as 

 A. von H eider (1879) made, is absolutely untenable. O. and R. Hertwig maintained already, that 

 the term "Filamentsepta" was not appropriate, as the fertile mesenteries also bear filaments. If this 

 declaration was already justified at a time when knowledge of the filaments was so imperfect, such 

 a division is still less defensible after my account of the filaments below has been made public, for 

 we do not really find as a rule, with reference to the filaments on sterile and fertile mesenteries, 

 any fundamental difference but merely one of degree. For both a ciliated tract region (spirocyst- 

 glandular tract with ciliated tracts) and cnido-glandular tract region are found in general alike on the 

 sterile and the fertile mesenteries. An exception however to this rule occurs in the genus Arach- 

 iid it tints and also, it seems, in P. ma.ua. O. and R. Hertwig further give expression to the conjecture 

 that possibly the sterile 1 ) mesenteries also become fertile later on. This is not the case however. 

 Still the fact must be emphasised that the difference between the mesenteries is not so sharp, if 

 irregularities occur in the arrangement of the mesenteries. Such is the case, for instance, in P. soli- 

 tarius, in which small but fertile mesenteries bear very wavy cnido-glandular tract regions and so 

 have a character approximating to the sterile mesenteries (Carlgren 1912 textfig. 43). 



Protomesenteries 2, the second couple reckoning from the directive plane are either sterile or 

 fertile; in the first case they resemble in point of length and structure the metamesenteries of the 

 third and fourth cycles. If on the other hand they are fertile they agree with the metameseuteries 

 of the first and second cycles. Fertile protomesenteries characterise the genera Cerianthus, Cerian- 

 thcopsis and Botrucnidifcr, sterile the genera Pachycerianthus, Arachnanthus (and Botruanthusl) 



Protomesenteries 3 which are immediately adjacent to the first metamesenteries, are always 

 sterile and resemble structurally the metamesenteries of the third and fourth cycles. 



The metamesenteries (= deuteromesenteries) as is already known are more or less clearly 

 arranged in 4 cycles (Faurot). Reckoning from the directive chamber we find usually a mesentery 

 of the ist cycle (M), next comes one of the third (B) which together form a macrobimesenterium 

 (macrobiseptum van Beneden): then comes a mesentery of the and cycle (m) and one of the fourth 

 (b) which together form a microbimesenterium (microbiseptum van Beneden). Exceptions to the 

 rule are Ccriantheopsis aincricanus and Botruanthus (see below). These four metamesenteries form 

 the first quartette (Faurot): then follows a second quartette, a third, and so on, which as a general 

 rule become shorter the more they approach the multiplication chamber lying directly opposite the 

 directive chamber. 



As a type for the arrangement of the quartettes, it has been customary to take C. membrana- 

 S, the species in which the quartette arrangement was first observed by Faurot (1891). A gradual 



') Me. Murrich (1910 p. 28) mentions, that in C. ambonen$is all metamesenteries are fertile. This would be a very 

 singular thing, if such were really the fact, in which case it would surely be necessary to set up a new genus although 

 Me. Murrich does not find it necessary. It must be noticed however, that both the specimens examined were in a very 

 bad state of preservation, so that it is necessary to get this statement confirmed before removing the species from the genus 

 Ceriantkus. Possibly there may be only a question of such irregularities as are found in P. solitarius. 



7* 



