THE MALAYAN SPECIES OE 0NYt!H0FH01lA. 78 



However this may be, it makes no difference in the number 

 of parts which constitute the head of Eoperipatus; for on 

 either view the head is composed of an archicerebral portion, 

 followed by the segment of the antennae, of the jaws, and of 

 the oral papilla3. 



VII. The Development of the Eye. 



The first rudiment of the eye appears as a small pit, situated 

 on the dorsal edge of the ectodermal thickening, which in 

 later stages gives rise to the brain (PI. 7, fig. 11a, e.). By 

 degrees the depression in question becomes deeper, and in 

 section presents the appearance of a fold of the ectoderm. 

 The canal putting its cavity in communication with the 

 exterior finally disappears. In fig. 25 a, on PI. 9, the 

 detailed structure of the rudiment of the eye at this stage 

 is shown. The position and arrangement of the nuclei is 

 interesting, those of the outer layer being arranged near 

 the cavity of the depi'ession, while those of the inner layer 

 are separated from the cavity by a layer of cytoplasm, which 

 presents the appearance of being divided into areas. This 

 layer of cytoplasm later on gives rise to the rods existing in 

 the adult eye. Soon after the obliteration of the canal, 

 which puts the cavity of the eye rudiment in communication 

 with the exterior, the outer layer is not in any way distinct 

 fi-om the overlying ectoderm, nor is the inner layer sharply 

 marked from the underlying brain rudiment (PI. 9, fig. 25 5). 

 The cavity of the eye is still small and quite empty, and the 

 nuclei situated on the inner side are beginning to arrange 

 themselves in layers with their long axes radially directed. 

 In the same figure the eye is shown as having been to some 

 extent constricted from the underlying brain rudiment. In 

 fig. 25 c on the same plate this constriction has been 

 carried much further, and the eye has been completely sepa- 

 rated from the ectoderm. The cavity of the eye is much 

 larger though it is still empty. Pigment is making its appear- 

 ance in the layer of cytoplasm situated on its inner side, and 

 distinctly marked by radiating lines. Simultaneously with 



