4.'>2 Avery E. Liiinhcrt. 



located cerebral area, the entire cephalic plate being raised into three 

 transverse ridges which are particularly prominent in the optic 

 region where they form the beginning of the optic ganglia (o. gl.). 



Between these rudimentary optic ganglia and the longitudinal 

 furrow on each side of the cephalic plate, the transverse ridges present 

 less conspicuous elevations, which form, in a similar manner, the 

 foundations of the cerebral ganglia (c. gl.). Thus we find in this 

 stage that the pre-cheliceral portion of the cephalic plate bears 

 three transverse segments, each segment consisting of a cerebral and 

 an optic portion, a condition which Patten found in both Acilius 

 and Buthvs (No. 35). 



The lateral invaginations, or grooves {lat. gr.), now liecome 

 deeper, folding inward until the result is the formation of a pit, 

 the blind end of which lies toward the median line underneath the 

 optic ganglia. 



At this time a thickened rim (o. pi.) appears on the outer margin 

 of the optic area on each side of the head. The sensory character 

 of this structure was first established by Patten (33 and 35) who 

 first observed it in Acilius, calling it the optic plate on account of its 

 relation to the future formation of the eyes. Later the same author 

 identified a similar structure in Buthvs and Mygale. 



Thus it appears that the cephalic plate of Epeira, anterior to the 

 cheliceral segment, from which it is still separated by a conspicuous 

 furrow on each side of the head, is composed of three distinctly 

 marked, longitudinal areas — a median area which constitutes the 

 foundation of the cerebral ganglia ; a marginal area, forming the 

 rudiment of the optic ganglia; and a thickened marginal rim, the 

 optic plate, which forms, at a later period, the retinal portion of 

 the anterior median eyes. 



The broad elevation of the ectoderm which has been already 

 recognized as the rudiment of the rostrum, has now formed two sepa- 

 rate prominences {ros.). These prominences have shifted down- 

 ward from the anterior margin of the head and lie between the 

 cerebral ganglia. A slight depression of the ectoderm, or ecto- 

 dermal pit, between the two rostral elevations indicates the begin- 

 ning of the stomodseum {st.). 



