Miscellaneous. 365 



2. A second lamella, which the author, like Prof. Strieker, regards 

 as the true sensorial lamella. 



3. A third lamella, which corresponds to the motory germinal 

 lamella of the higher Vertebrata. 



4. A fourth lamella, the analogue of the glandular or trophic 

 lamella {Troj>lmhlatt of Remak). 



In Pdohates the primitive streak does not precede the dorsal fur- 

 row, but appears at the same time as the latter : these two parts 

 are at first visible only in the posterior half of the dorsal region of 

 the future embryo ; but the dorsal furrow" is soon completed, when 

 its form is characteristic, and most frequently the primitive streak 

 cannot be distinguished in its anterior half. The clear surface has 

 an ovoid form ; its anterior limit corresponds to a dark zone which 

 shows itself at the same time as the dorsal furrow and primitive 

 streak ; this is the cephalic crescent, of which the subsequent modifi- 

 cations are very remarkable in Pelobates. 



The microscopical examination of transparent sections shows 

 clearly that, in Pelobates, the production of the dorsal furrow is 

 effected solely at the cost of the outer lamella (enveloping mem- 

 brane). This latter behaves like the sensorial lamella of the higher 

 Vertebrata at the period of the formation of the nervous canal; only, 

 when the dorsal furrow is closed, the tube produced by this closure 

 is not yet the nervous canal, which is afterwards completed by the 

 incurvation of the thick part of the sensorial lamella. 



At its anterior part the thickened portion of the sensorial lamella 

 not only gives origin to the cerebral cells and ocular vesicles, but, 

 after the occlusion of the nervous canal, there remains, on each side, 

 an aggregation of cells which become the origin of the auditory 

 vesicle and of the nervous part of the olfactory organ. The latter 

 becomes the olfactory lobule, which therefore is not, in Pelobates, an 

 excrescence of the anterior cerebral cell, and only comes into contact 

 with this gradually. 



As regai'ds the motory germinal lamella, we shall only saj' here 

 that the cutaneo-dorsal lamina) are not derived from the peripheral 

 portion of this lamella, but are prodiiced in their place by the laminae 

 of the primitive vertebra3. The dorsal cord, the "Wolffian bodies, 

 and the external and internal branchiae originate from the motory 

 lamella. 



Lastly, the author believes we may regard as the fii'st rudiments 

 of the kidneys two small masses of cells formed at the expense of the 

 glandular lamella ; but he has been unable to ascertain what relation 

 there exists between these organs and the excretory ducts of the 

 Wolffian corpuscles. — Mem. cle VAcad. Boi/. de BeJgique. Abstract 

 communicated by the Author. 



On the Systems of Caj)illari/ Vessels in the Gasteropods. 

 By Prof. Wedl. 



The doctrines that are now generally accepted in France and 

 elsewhere with regard to the blood-vascular system of the Mollusca 



