ON T?IE DEVELOPMENT OF LTMULUS LONGISPTNA. 79 



to the ganglin <if tlie median e3^es, arid the slender stalk which con- 

 n3c|-s this are.i with the retinal portion to the optic nerve. 



I was nnahle to study the later cluinges of the median eyes. 

 Their developineut i^'reatly l:)g's hehind that of the lateral eves. T do 

 not know wlictlier the anterior end of tlie retinal cells is mor|)ho]og-i- 

 cnlly the anterior end or not. The nn])aired retina] portion is after, 

 wards divided into two and gives rise to two median eyes in the adidt. 

 That the median eves of lAmulus are homologous with those of the 

 Ayachiiithi is most prol)al)le ; but it is a little doubtful whether they 

 are exactlv liomologous in every respect. Thus the median eye of 

 Limiihis ap])ears -is a tliickening anterior to the brain and outside the 

 semi-circii]:u' cejihalic groove, wliile llia.t of the Arachnida appears as a 

 thickening at tlie jiosterior end of the semi-circular cephalic groove. 



I find no more eves tlian the two ])airs mentioned above, nor 

 unv otlier structure which I can consider as homologous with them. 



Alimentary Canal. 



The stomodaeum is first of all ])i'<vliiced as a shallow round 

 invagination in the ce]>lialic lolie (figs. 10, 20, sfoiii.). 'Hw invagi- 

 nation becomes gradually deej) and takes an anterior and u])\vai-d 

 course (figs. .50, 68). When it almost reaches the dorsum it bends a 

 little backwards. At first it develops with Wie surrounding mesoblast 

 between the epiblast and the yolk-liypol)last (fig. 50); but later, the 

 volk finds its wav into tlie region in front of the stomodaeum, so that 

 in sections, we find masses of yolk before the stouK^daeum (fig. 52, 

 C+l: and fif. 56). The stomoda-al wall consists of hi^-h columnar 

 cells (figs. 45, 68). The stomodaeum gives rise to the œsophagus 

 and proventriculus. As the upper lip grows posteriorly, the mouth- 



