86 ALICE L. EMBLETON ON THE STRUCTURE AND 



lluuniug through the dorsal region of the cord, emhedded m the cellular coat, is a 

 structure which Greeff refers to as the " central canal," in spite of its excentric 

 position (PI. 9. figs. 28, 32, c.ii.). Spengel calls it the '' Neuralkaniile," and says : " Ein 

 Gebilde problematischer Natur namlich eiuen Langskanal, der dicht unter der dorsalen 

 Mittellinie verlauft," but how far it runs he is not able to say. Greeff, however, observes 

 of it : " Dieser Kanal aber communicirt mit der Leibeshohle, ist ein Theil derselben, der 

 zuni'ichst aus dem, vvie wir oben gesehen hal)en, mit dem Blutgefass-system in directer 

 Verbiudung stelienden Kanalsysteme des Riissels hervorzugehen scheint." 



In all my preparations, however, this " canal " has a similar structure and configura- 

 .tion to the so-called " giant fibres " of the Earthworm. I have in PI. 9. figs. 31, 32, made 

 comparative drawings of the dorsal region of the nerve-cord of Lmnbricus and of Echiuriis 

 imicinctus, both preserved and stained in the same way (Ehrlich's luematoxylin and eosin 

 or orange gave the most satisfactory results). Though Liimbriciis has three such 

 structures and Echiurus but one, the identity is very striliing. The same reagents, used 

 on the nerve-cord of Echim-us Pallasii, gave results as in the two former cases. In the 

 Earthworm, however, it was possible to trace the connection between the ganglion-cells 

 and the " giant fibres,"* being much more difficult to find with the central " fibre" than 

 with the lateral ones. Partly I could trace the connection in Echlurus uiiicinctus, though 

 not in such a way as to render the fact beyond dispute. 



Anal J'esicles. — Situated at the posterior end of the body-cavity is a pair of very 

 . characteristic organs, generally known as the " anal vesicles," though they are occasionally 

 referred to as the "posterior nephridia." 



In general form and histological structure, these vesicles show almost complete 

 agreement with those of Echiurus Pallasii as described by Spengel. The observations 

 were carried out with difficulty owing to the highly-contracted condition of the vesicles. 

 J)rasche evidently met with tlie same obstacle, for the only mention he makes of these 

 -organs is that " in beiden Exemplaren von brauner Farbe, liessen wegen ihres 

 macerirten Zustandes nur schlecht die Wimpertrichter erkeunen." However, in my 

 specimens the ciliated funnels are quite recognizable, even in a piece of a contracted 

 vesicle, Avhich was very slightly stained with alum-carmine and then clarified in oil of 

 cloves. Under the microscope this preparation had the appeai-ance of a mass of 

 diverticula, composed of very delicate tissue; the ciliated funnels (PI. 10. fig. 33,/.), 

 which took the stain rather more deeply than the surrounding tissue, were plainly observ- 

 able among the diverticula (rf.). Under a higher magnification the component cells could 

 be made out : those forming the diverticula jwssess very little protoplasmic contents, the 

 nucleus lying apparently in a vacuole (fig. 34, d. & nu.) ; but the cells forming the funnels 

 contain much granular protoplasm [pit-] very slightly vacuolated, and nuclei which 

 stain darkly {c.c. & /.). 



Among the numerous specimens I examined, occasionally there occurred vesicles not 

 wholly contracted ; and such a piece of uncontracted material, treated with the same 

 reagents as before, shows the vesicle-wall smooth and unfolded, as in fig. 35. The wall 



* Cy. Friedliinder : " Bcitriige zur Kenntnis des Cciitraluervensvstems von Lumhricas,'' Zeitsclir. f. wiss. Zool. 

 M. xlvii. 188«. 



