236 Miscellaneous^ 



course, which termiuates at the penis, it is | or sometimes 5 millim. 

 The narrow portion of the duct is pellucid ; the dilated portion, of 

 an opaque white, is composed of the same layers which are met with 

 in the JiageUum of the Helices. Beneath an external cellular mem- 

 brane we find a muscular membrane, followed in its turn by a 

 glandular layer, which does not exist in the narrow part of the duct. 



In the wide portion of the same organ we observe numerous lamelloB 

 arranged like the spiral fibre of tlie tracheae of plants. These lamellse 

 extend in an oblique spiral between the two margins of this portion of 

 the canal, their obliquity increasing towards the point of junction of 

 the two portions of the latter, in the neighbourhood of which they 

 finally become longitudinal. At the breeding-time they are covered 

 with solid white particles, which effervesce with hydrochloric acid. 



In its movement of retroversion the penis is followed by the 

 inferior deferent canal, which contains the eapreolus until the 

 moment when this body is expelled. — Comptes Renclus, November 4, 

 1872, tome Ixxv. pp. 1126, 1127. 



On the Developmental History of Petromyzon. By A. Schneider. 



Since August Miiller published his fine discovery of the transforma- 

 tion of Ammoco'tes into Fteromyzon (Miilhr's Archiv, 1856 ; see also 

 Ann. & Mag. N. H. ser. 2, vol. xviii. p. 298), every zoologist must 

 certainly have been desirous of witnessing this wonderful metamor- 

 phosis. Here in Giessen the opportunity seemed to offer itself to me ; 

 for, in the Bieberbach, Aminoc^cies branchialis occurs in such abun- 

 dance that in the course of two years I obtained about two hundred 

 Ammocoetes and a dozen of Petromyzon Flaneri. But I never obtained 

 the transition-stages, nor could I succeed in getting full-grown speci- 

 mens of Ammocoetes to undergo any further development in tanks. I 

 must therefore acknowledge witli thanks that Prof, von Siebold had 

 the kindness to give me two specimens of the transition-stage which 

 were in his possession. As I was sufficiently familiar with the struc- 

 ture of Ammocoetes and Petromyzon, these sufficed to give me an in- 

 sight into some of the most important processes. 



On the ventral surface of the Ammocoetes there is an elongate-oval 

 organ, already mentioned by Ilathke, which was regarded by A. 

 Miiller as the rudiment of the tongue, but the structure of which 

 has hitherto remained entirely unknown. It is a gland which opens 

 into the oesophagus in the ventral line between the third and fourth 

 branchial clefts. Its structure differs from that of all other known 

 glands. The orifice leads into two tubes lying close to one another, 

 and which extend forward to the end of the branchio-ocsophageal 

 cavity, and backward to the boundary between the fifth and sixth 

 branchial clefts. Just at the orifice another tube branches off' on 

 each side, passes a short distance backward, and then, bending up- 

 ward and forward, reaches the vicinity of the orifice of the gland, 

 then again bends downward and backward, and again downward 

 and forward, so that it describes about 1^ spiral convolution. In 

 the part situated in front of the orifice of tlae gland, there are on 

 each side four cords consisting of nucleated cells. The cells are cu- 



