102 BULLETIN OF THE 



PLATE X. 



Sections illustrating the development of the eye8. 



The four pairs of eyes are called according to their positions : anterior lateral, 

 anterior median, posterior lateral, posterior median. 



Fig. 63. A sagittal section showing an early condition of an anterior median eye, 

 — a thickened mass of " hypodermis " cells with the beginning of an 

 invagination. X 430. 



" 64. Sagittal section of an anterior median eye after the invagination is fully 

 established, three or four days before hatching. X 430. 



" 65. A frontal section through the anterior median pair of eyes, showing the 

 narrow lumen of the Invagination and its limited lateral extension. 

 X about 300. 



" 66. An older stage (one to two days before hatching) showing an elongation 

 on the part of the " hypodermis " cells which constitute the " vitreous 

 body," and also the closure of tlie invagination. X 430. 



" 67. A sagittal section passing through an anterior and a posterior eye of the 

 same side, two days after hatching. X 430. 



" 68. Sagittal section through an anterior median eye one day before hatching. 

 X430. 



" 69. Sagittal section through an anterior median eye, eight days after hatch- 

 ing ; the retinal portion has not yet reached its full devolopment. 

 X about 360. 



PLATE XI. 



Fig. 70-72, 77, 78, show the gradual headward concentration of the nerve bands. 

 Fig. 77 represents the earliest stage, in which the nerve bands reach 

 nearly around the egg; Fig. 72 shows the nervous elements con- 

 tracted so as to occupy only the folded ventral region ; in Fig. 71, the 

 abdominal cord is shortened considerably more ; Fig. 70 represents 

 the ventral ganglia concentrated within the thorax ; Fig. 78 shows 

 the condition of the brain and ventral ganglia at the time of hatching. 



70. Sagittal section approximately in the median plane, from an embryo 

 about two days before hatching. 



71. Sagittal section through the brain and nervous ganglia at about the com- 

 pletion of reversion. X 110. 



72. Sagittal section through the nervous system at the stage of the formation 

 of the proctodaeum. X 100. 



73-76 show four successive stages in the formation of the lungs, all magnified 

 about 300 diameters. 



73. View of the right-hand surface of a sagittal section of the lungs in an 

 early condition (about the middle of the period of reversion), showing 

 the nuclei arranged in parallel rows. 



