in the Hrain of the Ammoccete. 4!KI- 



Considering how much attention has of late years been devoted to- 

 the study of the Lamprey's brain, it seems almost incredible that such 

 definite structures as the cilia ted grooves described above should have 

 hitherto escaped observation. I have, however, been unable to find 

 any reference to them in the literature available. It remains to be 

 seen whether or not they occur in the adult. I am inclined to think 

 that they probably disappear when the development of the first choroid 

 plexus renders their presence no longer necessary, and such circulation 

 of the fluid in the cavity of the brain as is requisite may be safely left 

 to the cilia lining other parts. Ahlborn* figures a transverse sectioir 

 of the brain of Pefoomyzon planeri taken in the region of the posterior 

 commissure, but makes no mention of the structures in question. 

 Gaskellf also figures a transverse section through the corresponding 

 region of the brain of what he terms " an Ammoccetes immediately 

 after its metamorphosis," without giving any indication of the ciliated 

 grooves. It seems highly probable, then, that they are really absent 

 in the adult animal, and that their loss is to be looked upon as another 

 of those striking changes which accompany the transformation of the 

 larval Ammoccetes into the adult Petrvmyzon in Europe, or the closely 

 allied Geotria in New Zealand. 



Much more remarkable than the apparent absence of the ciliated 

 grooves in the adult is the fact that they seem, so far as I have been 

 able to discover, to have entirely escaped the notice of those investiga- 

 tors who have so minutely described the development of the Lamprey. 

 Thus in the beautiful memoirs of Shipley} and Scott^ I can find no- 

 reference at all to any such structures. 



The general appearance and structure of the ciliated grooves 

 forcibly call to mind the occurrence of more or less similar organs in 

 other divisions of the animal kingdom. We may, for example, com- 

 pare them physiologically with the siphonoglyphs of Alcyonarians, 

 the ambulacral grooves of Echinoderms, and the endostyle of Amphi- 

 oxus and the Tunicates. It is generally admitted that the function of 

 all these organs is to bring about the movements of fluids in definite 

 directions, and by analogy we may, I think, pretty safely conclude 

 that a similar function is performed in the case under discussion, 

 is also tempted to institute a physiological comparison with the ciliated 

 tubes in connection with the brain of the Nemertines, but in the present 

 state of our knowledge such a comparison can be of but little value. 



* Ahlborn, " Untersuchungcn iiber das Gehirn cler Petromyzonten," Zeit. 

 Wiss. Zool.,' vol. 39, p. 191, Plate 14, fig. 26. 



t Gaskell, "On the Origin of Vertebrates from a Crustacean-like Anee*t< 

 ' Quart, Journ. Micros. Sci.,' vol. 31, N.S., p. 379, Plate 25, fig. 3. 



t Shipley, " On some Points in the Development of Petromyzon fin 

 1 Quart. Journ. Micros. Sci.,' vol. 27, N.S., p. 325. 



Scott, " Notes on the Development of Petromy/.on," ' Journal of Morplu 

 vol. 1, p. 253. 



