THE EYES OF SPIDERS 



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although inverted with respect to the constituent parts of the cells, are 

 still simple in type, i.e. the retina consists of a single layer of sensory cells. 

 In some types there is a definite tapetal layer which reflects the light on to 



Section of one of the median eyes of the king crab, Limulus polyphemus, showing 

 the transparent chitinous lens, which fills the optic pit and is continuous 

 with the surrounding chitin which forms the head-shield or carapace. The 

 optic pit is lined by a layer of columnar cells (vitreous layer), which are 

 continuous with the surrounding hypodermal cells. Immediately beneath 

 this layer is a loose tissue consisting of branched connective tissue cells (ct.c), 

 some of which contain pigment, and a few rounded or oval cells of an epithelial 

 type (ep.c). Embedded in this tissue are the retinuke (ret.), which consist of 

 groups of five to seven large pear-shaped, epithelial cells arranged round a 

 refractile axial rod, called the rhabdome. Each retinular cell is continuous 

 with a nerve fibre (n.f.), which joins with similar nerve fibres to form the 

 main optic nerve of the median eye of the same side. 



