1890.] Development of the Atrial Chamber of Amphioxus. 81 



me to publish in my own name a summary of the results which I have 

 obtained under his guidance. 



Amphioxus occurs in great numbers in a comparatively small lake, 

 or pantano, which is situated behind, and separated from the sea by, 

 the village of Faro, near Messina. It is connected with the Straits 

 of Messina by a narrow canal, some two or three hundred yards in 

 length. 



The bottom of the pantano, in contrast to that of the Straits, 

 consists of foul mud ; and it may be mentioned in this connexion, as 

 I was informed by Professor Kleinenberg, that Amphioxus is only 

 occasionally met with in the Straits, and is entirely absent from 

 another larger pantano which lies behind the neighbouring village of 

 Ganzirri, and is joined by a short canal to the one at Faro. 



The embryos float on the surface, and are to be had by dredging on 

 the surface at sunrise, but the readiest method of obtaining them in 

 quantity is to take the adults in glasses and allow them to spawn 

 there, if they will. Spawning takes place about an hour after sun- 

 down. 



The ova, if fertilised, must be very carefully distributed among 

 several glasses containing clean, but unfiltered, water from the 

 pantano. If the water is filtered, or if sea water is employed, or if 

 too many ova are placed in one glass, they will certainly either die or 

 develop abnormally. 



The first outward and visible sign of fertilisation is the separa- 

 tion from the egg-cell of the yolk-membrane (Dottermembran) . 



Most, if not all, of the ova that I obtained were discharged through 

 the atriopore. 



If Kowalewsky* had not seen them issuing from the mouth, it 

 would not have been easy to understand how they could pass into the 

 pharynx in opposition to the constant outflow of water between the 

 gill- bars. 



Segmentation always commences at dusk between the hours of 

 seven and eight and goes on very rapidly through the night. 



The early stages have been so fully described by Hatschekf that I 

 will only refer to them in the briefest manner. 



At 8 P.M. segmentation commences ; at 11 P.M. invagination com- 

 mences ; at 1 A.M. the gastrula is complete ; at 3 A.M. the gastrula 

 begins to revolve by cilia within the yolk-membrane ; and at 5 A.M. 

 two pairs of myoccelomic pouches have been formed, and the embryo 

 ruptures the egg-membrane and becomes free-swimming. 



During the first day the embryo grows in length and adds several 

 pairs of somites. By about eight o'clock on the second morning, that 



* " Entwick. des Amph. lane." (' Mem. Acad. Imp^r. des Sciences de St. Pe"ter- 

 bourg,' Series VII,. vol. 11, 1867.) 

 t Claus's ' Arbeiten,' 1881. 

 VOL. XLVIII. O 



