XU CON'lENTS. 



PACE 



III. DEVELOPMENT OF AMPHIOXUS ......... 104 



Embryonic Development 105 



Fertilisation and Segmentation of the Ovum 105 



Gastrulation 109 



Growth of Free-swimming Embryo 113 



Development of Central Nervous System iiS 



Origin of INIesoderm and Ccelom 120 



Origin of the Notochord 124 



The Prjeoral " Head-cavities " of Amphioxus 126 



Endostyle and Pigment Granules 129 



Larval De\'elopment 130 



Formation of Primary Gill-slits, etc 130 



Formation of Secondary Gill-slits 135 



Club-shaped Gland and Endostyle 13S 



Continued Migration of Primary Gill-slits 139 



Peripharyngeal Bands 140 



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



The Adjustment of the Mouth, etc 143 



Equalisation of the Gill-slits 14S 



Further Growth of Endostyle, etc 149 



Development of Reproductive Organs 151 



General Considerations 155 



Larval Asymmetry 155 



Explanation of Asymmetry of Mouth and Gill-slits .... 1^7 



Larval Asymmetry not Adaptive and not Advantageous . . . 161 



Amphioxus and Ammoccltes 163 



Nervus Eranchialis Vagi 163 



Stomodreum, Hypophysis, and Gill-slits 165 



Endostyle or Hypobranchial Groove 167 



Peripharyngeal Ciliated Bands of Ammoccetes 16S 



Thyroid Gland 169 



Morphology of Club-shaped Gland of Amphioxus 1 70 



Prceoral " Nephridium " of Hatschek 172 



Ancestral Number of Gill-slits 173 



Notes .....,,,. 174 



