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WHEELER. [Vol. VIII. 



and the second protocerebral lobe there is a fissure (w) which 

 extends in some distance. Examination of a number of succes- 

 sive sections and stages has convinced me that this fissure is 

 not the result of artificial rupture during sectioning but that it 

 is brought about by an infolding of the intraganglionic thicken- 

 ing. The shape and position of the involuted mass may be 

 clearly seen from the surface in Stages H and I (see Figs. 8 

 and 9, igl^. 



In the frontal section (Fig. 39) are shown the relations of 

 the protocerebrum to the outer brain-segments and to the 

 ventral cord. Only a small portion of the optic plate {c) is 

 cut. Beneath it lies the optic ganglion (/^i \p-g^^ the small 

 cells of which contrast with the large cells of the brain proper. 

 The second protocerebral lobe {pc'^) still contains many neuro- 

 blasts which are budding forth their last progeny. The older 

 daughter-cells have already assumed an irregular arrangement. 

 The brain is separated from the attenuated dermatoblastic, or 

 integumental layer {db) beneath which the outer neurilemma 

 {enl) is forming. The inner neurilemma (iiil) envelops the 

 Punktsubstanz portions of the brain. The broad supraoesoph- 

 ageal commissure {s. cm) connects the third protocerebral lobes 

 of the two sides. As shown in the figure, the deutocerebrum 

 is distinctly praeoral. At an is shown the point where the 

 antennary nerve leaves the fibrous portion of this brain seg- 

 ment. Caudad to the deutocerebrum lies the tritocerebrum, 

 a pair of somewhat smaller ganglia united by the infraoesoph- 

 ageal commissure. It is this segment which according to 

 Viallanes innervates the labrum and the frontal ganglion. Be- 

 sides the supra- and infraoesophageal commissures and the 

 connectives which arise in the third protocerebral lobes and 

 traverse the deuto- and tritocerebrum to pass into the man- 

 dibular ganglion and thence through the nerve-cord, I may call 

 attention to two other masses of Punktsubstanz which lie in 

 front of the supraoesophageal commissure. These are shown 

 at /. in the figure. They appear to be connected by a small 

 band running parallel to the robust supraoesophageal commis- 

 sure. I did not succeed in finding these connected Punktsub- 

 stanz masses in all embryos of this stage, and as they were not 



