310 S. WATASE. 



oftlic optic norvo fibres is furtlier shown in Fig. 43, PI. XXXII. 

 The figure shows an oblique transverse section through the 

 onuiiatidial region of a more advanced embryo than the one 

 shown in Fig. 4!^hi, Pi. XXXIII. The piano of section passes 

 through the t>mmatidial area and through tiic bundle of the optic 

 nerves, which run forward. The migration of tiie ectodermal 

 cells seems to take place from the periphery to the inside of the 

 body. The basement membrane (/>. il/) forms a continuous 

 sheath around this migratory stream of ectodermal cells. 



In Fig. 40, PI. XXXII, is shown an embryo in the so-called 

 " trilobite stage." A pair of round protuberant organs {D. O) in 

 front of the eyes [E) are the " dorsal organs." The eye is distinctly 

 marked in this stage, owing to the formation of pigment granules 

 in the component cells. Except in the general enlargement of 

 the organ and the formation of the pigment granules in the 

 cells, the eye in this stage does not offer any material difference 

 from the condition seen in the stage which we have already 

 examined (Figs. 47-5t>). After the first moult of the chitinous 

 covering from the condition represented in Fig. 40, PL XXXII, 

 it passes into a more advanced condition when the essential 

 Limuloid features characteristic of the adult become distinctly 

 discernible. Fig. 41, PI. XXXII, represents the young Limulus 

 at its first stage in the acquisition of the external Limuloid 

 features. The whole body is translucent; the chitinous covering 

 of the body is yet extremely thin, and the dendritic ramifications 

 of the "liver" containing the renmant of the food-yolk of various 

 hues, sometimes green, at other times j'ellow or pink, shine 

 through the transparent tissues of the body. 



The compound eye {E) shows an interesting feature in con- 

 nection with the formation of the ommatidial area. 



Figs. 57-64, PI. XXXIV, show a series of transverse sections 

 throuirh the compound eve in the stage shown in Fig. 41, PI. 

 XXXII. ' 



Fig. 57, PI. XXXIV, represents a section passing tlirough the 

 anterior part of the eye. The ectoderm in the ommatidial area 

 is thrown into a number of folds. The cells lying in the valley 

 of the fold are destined to give rise to the ommatidium. In the 

 dorsal margin of the ommatidial area there exists a thick layer 

 of ectoderm, consisting of a number of large cells, each with 



