4.92 EXTERNAL ANATOMY OF INSECTS. 
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 variessmuch. Sometimes they are placed nearly 
in the segment of a circle, as in those spiders that have 
six eyes only, before noticed *; sometimes in two straight 
lines >; at others in two segments of a circle °; at others, 
in three lines 4, and at others in four *. Again, in some 
instances they form a cross, or two triangles ‘ ; in others, 
two squares £; in others, a smaller square included in a 
large one; in others, a posterior square and two anterior 
triangles‘; and sometimes a square and two lines. Though 
generally separate from each other, in several cases two 
of the eyes touch *; and in one instance three coalesce 
into atriangle!. But it-would be endless to mention all _ 
the variations, as to arrangement, in the eyes of spiders. 
2. Conglomerate Eyes™ 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 
Lepisma, the Iulide, and several of the Scolopendride. 
In Lithobius forficatus the eye consists of about twenty 
Segestria perfida, Walck. Aran. t. v. f. 52, &c. 
Tetragnatha and Latrodectes, Ibid. t. vii. f. 64. and t. 1x. f. 84. 
Nyssus coloripes, Ibid. t. vi. f. 58. 
Dolomeda, Ibid. t. ii. f. 18, 20. 
© Sphasus, Ibid. t. ii. f. 24. 
Mygale avicularia, Ibid. t. i. f. 3. 
aoa 8o fF B 
» 
€ Sparasus, Ibid. t. iv. f- 41. Prare XXVI. Fic. 37. 
h Eresus, Ibid. t. iii. f. 26. i Storena, Ibid. t. 1x. f. 86. 
« Argyroneta, Ibid. f. 88. 1 Pholeus, Ibid. t, yi. f. 80. 
me 
5 
Piate XIII. Fie. 11. 
