Segments of a Lobster. 



99 



FIG. 56. 



four openings on the under sidethe mouth, the anus 

 in the middle line of the last joint of the tail on the 

 under surface, and the paired openings of the egg- 

 producing organs at the base of the third pair of walk- 

 ing limbs. Through these the eggs are extruded, and 

 are carried in clusters under and around the bases of 

 the hind series of feet. 



In the large anterior mass of the body, sheltered 

 by the dorsal shield, there are fourteen segments 

 united, comprising the head, 

 thorax, and abdomen. The 

 head segments bear their six 

 pairs of appended limbs, the 

 first pair of which are modi- 

 fied into stalks for the eyes, 

 which are remarkable organs, 

 each consisting of a large 

 number of rods of a crystal- 

 line appearance, each placed 

 at the end of a nerve fibril or 

 thread, and surrounded 

 by a mass of pigment. The 

 of the optic nerve pass in 

 and each fibril ends in its crystal rod, the mass of 

 rods being arranged in a cluster, slightly divergent 

 so as to exhibit a rounded outer surface, over which 

 the chitinous skin extends as a fine, perfectly trans- 

 parent covering. The eye stalk is two- jointed. 



The second pair of limbs are feelers called the 

 antennules or lesser antennae, consisting of three 

 basal joints, terminated by a pair of slender processes 

 each made up of many little rings ; these are followed 



Vertical section through the eye 

 of an Insect, showing the stalk 

 or optic nerve, the white radiat- 

 ing lines or secondary optic 

 nerves and the crystal cones. 



numerous united fibrils 

 the centre of the stalk, 



