x ii CONTEXTS. 



PAGE 



III. DEVELOPMENT OF AMPHIOXUS 104 



EMBRYONIC DEVELOPMENT .............. I0 5 



Fertilisation and Segmentation of the Ovum ....... 105 



Gastrulation .................. IO 9 



Growth of Free-swimming Embryo .......... "3 



Development of Central Nervous System . . , ..... 118 



Origin of Mesoderm and Ccelom ..... .... 120 



Origin of the Notochord ... .... 124 



The Pneoral " Head-cavities " of Amphioxus ...... 126 



Enclostyle and Pigment Granules .......... I2 9 



LARVAL DEVELOPMENT ............... J 3 



Formation of Primary Gill-slits, etc .......... J 3 



Formation of Secondary Gill-slits . . ....... J 35 



Club-shaped Gland and Endostyle .......... !3 8 



Continued Migration of Primary Gill-slits ........ 139 



Peripharyngeal Bands .............. I 4 



Atrophy of First Primary Gill-slit and Club-shaped Gland, etc. 140 



The Adjustment of the Mouth, etc ........... ! 43 



Equalisation of the Gill-slits ........... ! 4 8 



Further Growth of Endostyle, etc. *49 



Development of Reproductive Organs ......... IS 1 



GENERAL CONSIDERATIONS ............. J 55 



Larval Asymmetry .............. J 55 



Explanation of Asymmetry of Mouth and Gill-slits . . . 157 



Larval Asymmetry not Adaptive and not Advantageous . . . 161 



AMPHIOXUS AND AMMOCCETES ............ l6 3 



Nervus Branchialis Vagi .... ........ J 3 



Stomodceum, Hypophysis, and Gill-slits ........ l6 S 



Endostyle or Hypobranchial Groove . ....... l &7 



Peripharyngeal Ciliated Bands of Ammoccetes ..... 168 



Thyroid Gland ..... .... 169 



Morphology of Club-shaped Gland of Amphioxus . . . . 1 70 



Przeoral " Nephridium " of Hatschek ......... 1 7 2 



Ancestral Number of Gill-slits 



NOTES 



