CERIANTHARIA. 65 



4th cycles have much shorter ciliated tracts. This being so, the length of the ciliated tract region 

 stands in inverse proportion to that of the cnido-glandnlar tract region, as we shall see. The length 

 of the ciliated tracts varies considerably on the analogous mesenteries of the different species. 



The region of the cnido-glandular tract is always devoid of ciliated streaks. The cnido- 

 glandular tract is distinguished from the median streak in the ciliated tract region by the fact that 

 the epithelium contains numerous large thick-walled nematocysts 1 ) and numerous elongated, gra- 

 nular gland cells, in addition to which supporting cells occur, and more sparsely, homogeneous mucus 

 cells. The configuration of this tract in transverse section is always more or less tongue-like, never 

 flattened, and the mesogloea of the mesenteries terminates in the filament without ramification. The 

 muscles consequently, having no means of attachment to the slight mesogloeal lamella, are either 

 absent or extremely feebly developed. 



The region of the cnido-glandular tract, which answers to the single wavy coiled cnido-glan- 

 dular tract in Actiniaria, is best formed on protomeseuteries 3 and on the metamesenteries of the third 

 and fourth cycles, where it forms more or less folded (in A. oligopodiis, sarsi, (7. valdiviae, lloydti, B. 

 norvegicus] or very wavy bands. A close examination of the metamesenteries of the first and second 

 cycles and of protomesenteries 2 teaches us, however, that these mesenteries also for the most part 

 bear cnido-glandular tracts, though more feebly developed. This is the case at least with all the 

 Ceriantharia studied by me with the exception of the forms provided with van Beneden's "acontia", 

 that is to say, the genus Arachnanthus, and also the metamesenteries of the first cycle in P. maua. 

 Least developed are those on protomesenteries 2 and the metamesenteries of the first cycle in C. 

 iiiniibranaceus and C. americanus and on the metamesenteries of the first and second cycles in P.soli- 

 tarius. Better developed are those of the metamesenteries of the second cycle in C. membranaceus 

 and of the metamesenteries of the first and second cycles in C. lloydii. Yet how easily they escape 

 observation, may be inferred from the fact that no investigator has called attention to the presence 

 of these subdivisions of the filament on the above-mentioned mesenteries of the first and second cycles, 

 and on protomesenteries 2 in adult individuals. Van Beneden for instance did not see this tract 

 on the metamesenteries of the ist and 2nd cycles or on protomesenteries 2 in C. lloydii, as appears 

 from his not marking it in the diagram of his work (1898 fig. A, p. 25), nor mentioning it in discussing 

 (1898 p. 22) von Heider's "Filamentsepten" (cloisons a pelotons). On the other hand, van Beneden 

 did observe them in some larval forms (1898). It is probable enough that other investigators have also 

 noticed the cnido-glandular tract on these mesenteries as Me. Murrich in C. americanus -- but 

 in view of the very complicated and conflicting nomenclature of the divisions of the filament and the 

 usually imperfect descriptions of the filaments, this cannot be positively settled. 



The cnido-glandular tract, as has been said, is feebly developed in some species on the meta- 

 meseuteries of the first and second cycles, where it has the form of a straight or more or less winding 

 thread. The simplest case is found in P. solitarius, where the cnido-glandular tract on the meta- 



i) So-called spirocysts, thin-walled nematocysts, may occur here, but very sparsely if they do, just as, conversely, 

 thick-walled nematocysts may occur in the median streak on the boundary of the cnido-glandular tract. In rare cases thick- 

 waned nematocysts seem to occur in greater numbers in the median streak. This is the case in P. maua, where the cnido- 

 glandular tract is absent on the better developed metamesenteries 



The Danish Ingolf-Expedition V. 3. 9 



