298 M. A. Miiller on the Development of the Lampreys. 



XXVI. — On the Development of the Lampreys. 

 By August Muller*. 

 M. August Muller has observed some interesting facts in 

 the history of the small Lamprey, which occurs abundantly in 

 the fresh waters near Berlin. The animals appear suddenly at 

 the spawning season in clear brooks, where they glide about 

 amongst the stones, or, attaching themselves to these by the 

 mouth, float in the stream. After spawning they disappear 

 entirely ; and, during the period of their occurrence, none but 

 full-grown individuals are to be seen. 



At the spawning time they are seen in small groups of ten 

 or more individuals, and the spawning is effected in the fol- 

 lowing manner : — The male fastens with his mouth upon the 

 neck of the female behind the eyes, and then twists his body 

 half round towards her belly, when the emission of the ova and 

 seminal fluid takes place. 



The recently emitted ova are less than half a line in diameter, 

 white, slightly yellowish, and enclosed in a thin gelatinous 

 capsule, which is difficult of detection even after swelling in 

 water. The segmentation is complete, as already stated by 

 Schultzef, and commences about ten hours after fecundation. 

 The process is described much in the same terms as by Schultze : 

 the yelk is divided into a smaller upper, and a large lower por- 

 tion, from the former of which the embryo is developed; the 

 upper portion is composed of small, and the lower of large 

 masses, and the centre is occupied by a cavity, which afterwards 

 becomes smaller, and gradually draws towards the head of the 

 embryo. 



The hinder end of the egg becomes flattened, and on the 

 upper part of this flat space the anal opening makes its appear- 

 ance, surrounded in front and on the sides by a horse- shoe-shaped 

 ridge, and from this a narrow canal is soon traceable half across 

 the egg, beneath the region of the dorsal cord. The brain and 

 spinal cord then become more strongly developed ; they are 

 divided by a longitudinal furrow, which soon closes again. The 

 dorsal cord never advances further than between the labyrinths 

 of the ears. Its contents appear striated towards the period of 

 exclusion, as is also the case in the embryos of some bony 

 fishes; but in the Lamprey the strise consist of series of cells. 

 The head grows out, and exhibits two lateral swellings, separated 

 by a cleft in the middle. Above these is the cavity of the 

 mouth, and subsequently the nasal opening makes its appear- 

 ance, and gradually moves from the ventral to the dorsal surface. 



* From Miiller's Archiv 1856, No. iv. p. 32^1 Communicated by 

 W. S. Dallas, F.L.S. 



t See Annals, vol. xvii. p. 443. 



