EXPLANATION OF PLATES 31, 32. xliii 



Fig. i. Somewhat later stage, in which the primitive cumulus is still visible. 

 Near the opposite end of the blastoderm is a white area, which is probably the 

 rudiment of the procephalic lobe. 



Fig. 3# and 3^. View of an embryo from the ventral surface and from the side 

 when six segments have become established. 



Fig. 4. View of an embryo, ideally unrolled, when the first rudiments of the 

 appendages become visible. 



Fig. 5. Embryo ideally unrolled at the stage when all the appendages have 

 become established. 



Fig. 6. Somewhat older stage, when the limbs begin to be jointed. Viewed 

 from the side. 



Fig. 7. Later stage, viewed from the side. 



Fig. 70. Same embryo as fig. 7, ideally unrolled. 



Figs. 8a and 8/>. View from the ventral surface and from the side of an embryo, 

 after the ventral flexure has considerably advanced. 



Fig. 9. Somewhat older embryo, viewed from the ventral surface. 



PLATES 31 AND 32. 



COMPLETE LIST OF REFERENCE LETTERS. 



ao. Aorta, ab. g. Abdominal nerve cord. ch. Chelicerse. ch. g. Ganglion of 

 chelicene. ep. Epiblast. hs. Hemispherical lobe of supra-cesophageal ganglion. 

 At. Heart. /. /. Lower lip. m. Muscles, me. Mesoblast. mes. Mesenteron. mp.g. 

 Malpighian tube. ms. Mesoblastic somite, a*. CEsophagus. p. c. Pericardium. 

 pd. Pedipalpi. pd. g. Ganglion of pedipalpi. pr. Proctodseum (rectum), pr. c. 

 Primitive cumulus, s. Septum in abdomen, so. Somatopleure. sp. Spknchnopleure. 

 st. Stomodaeum. su. Suctorial apparatus. su. g. Supra-cesophageal ganglion. 

 th. g. Thoracic ganglion, v. g. Ventral nerve cord. y. c. Cells derived from yolk. 

 yk. Yolk. j. n. Nuclei of yolk cells. 



I g IV g. Ganglia of ambulatory limbs, i 16. Postoral segments. 



Fig. 10. Section through an ovum, slightly younger than fig. i. Shewing 

 the primitive cumulus and the columnar character of the cells of one half of the 

 blastoderm. 



Fig. n. Section through an embryo of the same age as fig. i. Shewing the 

 median thickening of the blastoderm. 



Fig. 12. Transverse section through the ventral plate of a somewhat older embryo. 

 Shewing the division of the ventral plate into epiblast and mesoblast. 



Fig. 13. Section through the ventral plate of an embryo of the same age as 

 fig. 3, shewing the division of the mesoblast of the ventral plate into two mesoblastic 

 bands. 



Fig. 14. Transverse section through an embryo of the same age as fig. 5, passing 

 through an abdominal segment above and a thoracic segment below. 



Fig. 15. Longitudinal section slightly to one side of the middle line through an 

 embryo of the same age. 



