296 ME. J. E. BUEBDEN ON 



the developing filaments is a condition of no morphological im- 

 portance, perhaps due only to the readjustment of the relations 

 between the oesophagus and mesenteries consequent upon the 

 disorganization of the central tissue and the formation of the oral 

 aperture. Any subsequent discontinuity in such a larva as that 

 from which fig. 21 is taken would clearly have no bearing on the 

 morphological value of the filaments. 



From the details revealed by the larva of Lehrtmia, I consider 

 that we are justified in regarding the simple filament of the 

 Madreporaria and Alcyonaria, and the glandular streak of the 

 trilobed filament of the Actiniaria, as representing a continua- 

 tion of the enteron ; a relationship already suggested by other 

 workers (p. 307). 



The fact that no such break in continuity as that referred 

 to has ever been observed between the oesophageal epithelium 

 and the lateral or ciliated streaks of the trilobed Actiniarian 

 filament, has led E. B. Wilson and McMurrich to regard these 

 as ectodermal downgrowths from the stomodseal walls, and in 

 this they are followed by most writers on the Actinozoa. My 

 results, however, incline me to the opinion of H. V. Wilson, 

 namely, that the simple Madreporarian filament is homologous 

 with the complex Actinian filament. 



Ontogenetically the Plimmerstreifen appear later than the 

 Driisenstreif, and, at any rate in Lehrunia, after the continuity 

 of the latter with the oesophagus has been established. They 

 are always highly specialized structures in that the constituents 

 are wholly columnar ciliated cells, without an admixture of 

 gland-cells and cnidoblasts, thus diff'ering histologically from the 

 flesophageal lining or median streak of the filament. There is 

 little doubt that they are, like the dorsal filaments of the Alcyo- 

 naria, special circulatory organs. Uciually they are most strongly 

 developed in colonial Actiniaria, such as the Zoanthidae. The 

 so-called " Eeflected Ectoderm " of Haddon (1891, p. 619) met 

 with in this family must, in all probability, be looked upon as a 

 strong!}' developed portion of the ciliated streak. 



To anticipate results yet to be published, I find that along the 

 two sides of the simple filament of the West-Indian species of 

 Madrepora a very characteristic structure is developed, in no way 

 histologically distinguishable from the riimmerstreifen of the 

 Actiniae. 



