t8 



X. KISHINOUYE. 



and in tlie embryonic stnges does not communicate with the brain. 

 From the ndiilt anatomy and from the aua](3gy of the spider, I 

 consider the p(3rtion of the l)rain formed by the external groove as 

 tiie optic ganghon of the lateral eyes. 



The lateral compound eye of Lwiulus is homologous uith the 

 o-roup of the lateral simple eyes of the Arachnida. For the lateral 

 simple eyes of the Arachnida arise as a group from a common epiblastic 

 thickening — as I have recently shown in the Döbutsugaku Zasshi 

 (the Zoological ]\lagazine, Japanese) and as is set forth in the article 

 immediately following in this Journal. The lateral eyes of the scorpion 

 are most nearly related io the lateral compound eye ol' Liiiiidus, 

 as they are monostichous and are placed close to one another. 



The median eves a})pear as paired invaginations in paired epiblastic 

 thickenings near the median line and in front <)f the cephalic thicken- 

 inc- (fig. 12). Thev are formed just outside the brain (tigs. 34, 38), 

 so that they are not neural in <)rigin. The paired invaginations after- 

 wards aj)pro;i('h each other (tig. 13). and hnally form a median unpnired 

 invagination (tigs. 14, 36, 37). This unpaired invagination becomes 

 deep and slender and develops anteriorly and dorsally, its blind end 

 touching the e[)i])last (figs. 50, 56). The lumen of the invagination is 

 lost as it becomes exceedingly slender, and at this stage the median 

 eves are represented Ijy a slender solid rod (tig. 51). Later the ex- 

 tremity of the rod becomes enlarged and at the same time epiblastic 

 cells lying on it Ijecomes columnar (figs. 56, 67). The enlarged 

 extremity Ijecomes the retina and tlie columnar ei)ithelium forms the 

 vitreous body. 



The mouth of the invagination is closed, when the tulje of the 

 invagination becomes solid. The epiblast where there was originally 

 the mouth of the invagination is thick and slightly depressed (figs. 

 6(S, 69). This thickened area of the epiblast probably gives rise 



