Miscellaneous. 4G3 



Researches upon some of the lower Marine Animals. 

 By 11. Letjckart and A. Pagenstechf.r. 



Under this title, MM. Leuckart and Pagenstecher have published 

 the results of some investigations made at Heligoland. The following 

 are some of the most interesting of these notes : — 



Amphioxus lanceolatits. 



The authors, like M. Schultze, have examined immature indi- 

 viduals of this interesting vertebrate animal ; but, while the latter 

 observer had only two specimens under his hands, they have been 

 able to collect a considerable number. They were struck by the 

 great want of symmetry which characterizes the young animals, — a 

 want of symmetry of which Johann Muller recognized traces in the 

 adult Amphioxus, and which has also been indicated by MM. 

 Schultze and Kolliker. It is manifested principally in the following 

 manner : — the mouth, the anterior branchial aperture, the olfactory 

 organ, and the eye are all situated on the left side ; the branchial 

 ridges are differently arranged to the right and left of the median 

 line; and the loop-like organs, of problematical signification, included 

 between them are also different. The dorsal portion of the animal 

 is perfectly symmetrical; and the great development which it acquires 

 in the adult animal gradually renders the want of symmetry in the 

 ventral region less apparent. 



The authors have ascertained that the chorda dorsalis of the 

 Amphioxus is provided with a longitudinal groove on its upper part, 

 so that its transverse section is cordate. In this groove is lodged the 

 inferior convexity of the spinal cord. The anterior extremity of the 

 medulla encloses a small cavity (a kind of ventricle), into which the 

 spinal canal opens. Perhaps, in this arrangement, we may see the 

 indication of a rudimentary brain. 



The number of branchiae varies between eleven and seventeen. The 

 new branchiae make their appearance behind those already in exist- 

 ence. They are all placed immediately beneath the alimentary 

 canal, without any direct communication with the latter. The ventral 

 wall of the animal is cleft along the median line in such a manner as 

 to allow the branchial apparatus to float freely in the sea. This long 

 fissure, which is called the posterior respiratory aperture by the 

 authors, allows the water which has been employed in respiration to 

 flow off. This respiratory apparatus of the young animal is easily 

 seen to be very different from that of the adult, as described by 

 Johann Midler ; it is probable that the respiratory apparatus of the 

 young animal becomes transformed directly into that of the adult by 

 the formation of a cartilaginous branchial skeleton, and the esta- 

 blishment of a direct communication between each branchia and the 

 interior of the intestine. At the same time, the fissure just indicated 

 must be closed in such a way as only to leave a single small aperture 

 — the abdominal pore of Midler. Close to the mouth, on the left 

 side of the animal, there is a fissure imperfectly seen by Schultze, 

 which the authors have ascertained to be the anterior branchial 

 aperture. 



