CHAPTER XXXVI. 



CEPHALOCHORDA. 



Amphioxus. 



The earlier statements concerning the development of Amphioxus 

 made by Max Schultze (No. 18), Leuckart and Pagenstecher 

 (No. 15) referred merely to a few of the later larval stages ; our 

 knowledge of the ontogeny of this form is, therefore, founded princi- 

 pally on the investigations of Kowalevsky (Nos. 10 and 11), and was 

 extended by Hatschek (Nos. 4 and 8). The metamorphosis of 

 Amphioxus has recently been described by Ray Lankester and 

 Willey (No. 13) and by Willey alone (No. 23). The develop- 

 ment of the genital organs has been investigated by Boveri (No. 3). 

 This last author (No. 2) as well as Spengel (No. 19), Ray Lankester 

 (No. 12) and van Wuhe have also published treatises on the anatomy 

 of the adult Amphioxus to which we shall have occasion to refer.* 



A. Oviposition, Cleavage and Gastrulation. 



The mature genital products of Amphioxus pass from the genital 

 chambers, through rupture of their walls, into the atrial cavity and 

 thence they were said to pass through the gill-clefts into the pharynx 

 and to be ejected through the mouth (Kowalevsky, Hatschek). 

 According to Ray Lankester and Willey, however, they are, in 

 most cases, ejected through the atriopore. Fertilisation takes place 

 in the surrounding water. The newly laid egg is surrounded by a 

 vitelline membrane at first only slightly separated from it, but, under 

 the influence of the sea water, the interval between the egg and the 



•[More recently, Sobotta (No. XI.) and Sticht (No. XII.) have rein- 

 vestigated the maturation and fertilisation of the egg, and the former, 

 Klaatsch (No. IV.) and Macbride (No. VIII.) have re-examined the forma- 

 tion of the germ-layer.— Ed.] 



