EXTERNAL ANATOMY OF INSECTS. 493 



these insects would be very limited ; but by means of the 

 structure just stated, they get a considerable range of sur- 

 rounding objects, as well as of those above them. With 

 regard to the arrangement of the eyes we are consider- 

 ing, it varies much. Sometimes they are placed nearly 

 in the segment of a circle, as in those spiders that have 

 six eyes only, before noticed a ; sometimes in two straight 

 lines b ; at others in two segments of a circle c ; at others, 

 in three lines d , and at others in four e . Again, in some 

 instances they form a cross, or two triangles f ; in others, 

 two squares s ; in others, a smaller square included in a 

 large one h ; in others, a posterior square and two anterior 

 triangles ' ; sometimes a square and two lines. Though 

 generally separate from each other, in several cases two 

 of the eyes touch k ; and in one instance three coalesce 

 into a triangle '. But it would be endless to mention all 

 the variations, as to arrangement, in the eyes of spi- 

 ders. 



2. Conglomerate Eyes m differ in nothing from simple 

 eyes, except that instead of being dispersed they are col- 

 lected into a body, so as at first sight to exhibit the ap- 

 pearance of a compound eye : — they are, however, not 

 hexagonal, and are generally convex. They occur in 



a Segestria perjida, Walck. Aran. t. v.f. 52. &c. 



b Tetragnatha and Latrodectes, Ibid. I. vii./. 64. and /. ix.f. 84. 



c Nyssus coloripes, Ibid. t. vi-f. 58. 



d Bolomeda, Ibid. t. u.f. 18, 20. 



e Sphasus, Ibid. t. m.f- 24. 



f My gale avicidaria, Ibid. t. \.f. 3. 



e Sparasus, Ibid. t. iv. /. 41. Plate XXVI. Fig. 37- 



b Eresus, Ibid. t. m.f. 26. l Storena, Ibid. t. ix.f. 86. 



x Argyroncta, Ibid.f. 88. ' Pholcus, Ibid, t. viii./. 80. 



m Plate XIII. Fig. 11. 



