1 882.] Recent Literature. 313 



But this cannot be confounded with the question of origin. On 

 this point the Darwinian is on the same footing as the old time 

 Creationist. The latter says God made the variations, and the 

 Darwinian says that they came by chance. Between these posi- 

 tions science can perceive nothing to choose. — C. 



RECENT LITERATURE. 



The Development of Amphioxus bv Hatschek. 1 — The entire 

 organic world does not contain a more interesting animal than the 

 lancelet, Amphioxus or Branchiostoma, the lowest vertebrate, 

 the link which, though far removed from either, indicates a com- 

 mon origin, or at least a remarkable structural similarity between 

 the Vertebrata and the Ascidians or Tunicates. 



The literature upon this creature, extensive but incomplete, is 

 now enriched by the present exhaustive memoir by one of the 

 most careful and accurate of European biologists. In this me- 

 moir, which forms the greater portion of a late issue of the 

 Arbeiten of the Zoological Institute of the University of Vienna, 

 and is illustrated by nine large plates, carefully drawn and 

 colored, the development of the lancelet is traced with the 

 greatest minuteness from the ovum to the adult. The ovum 

 of Amphioxus contains, between the germinal portion and the 

 enclosing membrane a remarkably large water space, forming 

 by far the greater portion of its bulk, and the cleavage is 

 very near regular, the difference between the size of the cells 

 separated by the first equatorial fissure being very small. The 

 "blastula" stage with its large segmentation cavity, and the 

 gradual formation of a " gastrula," are abundantly illustrated; 

 two plates are devoted to the more advanced development, plainly 

 showing the hollow structure and alternate position of the 

 muscle-plates or myocommas, and three colored plates are filled 



Until an advanced period of embryonic life, the digestive tract 

 is continuous with a dorsal canal, which terminates at an opening 

 upon the upper surface of the head. At a later period the vent is 

 formed, connection between the digestive tract and the dorsal 

 canal is cut off, the anterior opening closes, and the dorsal canal 

 becomes the neural canal. 



The hollow form of the muscular segments is shared by the 

 lancelet with the Selachians sharks and rays), Cyclostomes 

 (hags and lampreys) and Batrachia, and tends to prove their 

 Primary origin as diverticula from the digestive cavity. 



In the notochord vacuoles are developed, which become larger, 



