1905.] NATURAL SCIENCES OF PHILADELPHIA. 141 



cells of Lumbricus, epithelial sensory cells [Flemming's cells] of Mol- 

 luscs), giving greater efficiency at a certain spot, and that the internal 

 differentiations are but secretions or cytoplasmic differentiations due 

 to the specialized condition of the cell. Granting these facts, then, 

 sense buds are homologous of necessity only in their origin from an 

 epidermal tissue, although the homology may be greater. Since sense 

 buds are known which are sensitive to touch, taste, smell, sight and 

 vibration waves, it seems entirely unnecessary to assume that a light- 

 perceiving organ, such as an ommatidium, has arisen as a modification 

 of some other kind of sense bud, rather than that it arose as an accumu- 

 lation of epithelial cells already sensitive to light. 



Since we know that single cells are acted upon by light waves (e.g., 

 Protozoa), and that epidermal cells often give rise to nervous impulses 

 when acted upon by light (e.g., skin of the earth worm), there seems 

 no reason for assuming that the ommatidium has arisen other than by 

 an accumulation of such sensitive cells and then by invagination a 

 light-refracting organ has been formed over it. Such a view is directly 

 opposed to the view of Patten that the ommatidium is a hair-bearing 

 sense organ. As will be shown later, his theory is untenable on account 

 of the absence of the essential structure for such a homology the hair. 

 There is not only no indication of such an organ for the eye, but no 

 need for such a complicated theory of the origin of these organs, since 

 easy transition steps from a single cell sensitive to light to the omma- 

 tidium are obtainable and such an origin seems far more probable. 



Johansen (1893), in his description of the development of the eye of 

 Vanessa urticcz L., figures and describes a spindle-shaped mass of cells 

 which is the ommatidium of the pupa when two days and one hour old. 

 He has also observed the same spindle mass in the young pupa of 

 Sphinx euphorbia. This differs from what I have described for Apis 

 in that the corneal pigment cells and cone cells lie distal to the retinula, 

 and I am led to conclude that he has observed a stage just after the 

 sinking in of the retinula, a stage which I am unable to describe for 

 Apis. At any rate his conception of the morphology agrees with 

 mine, since the retinula is in the centre of the ommatidium and the 

 cone cells and corneal pigment cells are lateral to it. 



2. Pupa. 



During the so-called semi-pupa stage, just after the larva is 

 sealed up by the workers of the hive, and before the bee is a complete 

 pupa, very rapid growth takes place, and the eye increases still more in 

 size and becomes more and more differentiated until at the beginning 



