618 



C. O. WHITMAN, 



point, and their accuracy would not have been disputed had our author 

 taken the trouble usually expected of those who assume the right to 

 contradict. 



The origin of the sensory rudiments from the epidermis is clearly 

 shown in Fig. A, The section passes through the optic buds (Hand III) 

 and three median sense-buds, the metameric homologues of the eyes. 



At the tip are seen two or three ru- 

 diments of labial sense organs. In this 

 stage of development, the cells of the 

 buds show no histological differentiation ; 

 they are alike in origin, size, form, and 

 structure. 



Fig. B presents an early stage of 

 differentiation, which is reached about 

 the time the first trace of yellow^ pigment 

 can be seen. The future tactile cells 

 now have an elongated form, and they 

 occupy the upper and anterior angle 

 of the eye. The nuclei are smaller than those of the deeper, rounded 

 cells, which are destined to become the visual cells and the pigment-cup. 



Fig. B. A section of the prin- 

 cipal eye from a specimen 10 days 

 old. (X 780.) 



Fig. C. Sagittal section of a somewhat older individual (3—4 mm in length), showing 

 the eye in a more advanced stage of diflferentiation. 



In Fig. C we find the differentiation of parts carried out so far 

 that we have no difficulty in comparing them with the adult conditions 

 shown in Fig. D. The tactile and visual elements (e. 2) are clearly 



