STRUCTURE 



51 



nerves. With the nervous system we may mention the sense 

 organs, the eyes, which are present in most cases, though 

 wanting, as has been ahready stated, in many groups. They are 

 usually present as clusters of ocelli or eye spots closely packed 

 together, or (in Scutigera) as peculiarly formed facetted eyes. The 

 sensory hairs on the antennae must be reckoned as sense organs, 

 as also the tufts of sense hairs on the head of Polyxemis. Scuti- 

 gera has also a peculiar sense organ beneath the head, consist- 

 ing of a sac opening on the under side of the head full of 

 slender hairs, each of which is connected at its base with a nerve 

 fibre. Except the eyes, the Myriapod sense organs have usually 

 the form of hairs or groups of hairs connected with nerve fibres, 

 which communicate with the central nervous system. 



Tig. 31. — Under side of the head 

 of Scutigera coleoptrata, with 

 sense organ, eo, Opening of 

 sense organ to the exterior ; 

 0, sense organ shown through 

 the chitin ; m, mouth ; oc, 

 eye ; i^ixl, maxilla ; / furrow in 

 the chitin. (Heathcote, Sense 

 organ in Scictir/era coleoptrata. ) 



gang.c. 



ixt.eui. -y^''/' 



Fig. 32. — Highly magnified section through head 

 of Polyxenus lagurus, showing sense organ. 

 ext.out, external cuticle ; t, tube surrounding 

 base of sense hair; gang.c, ganglion cell. 

 (Heathcote, Anatomy of Polyxenus lagums.) 



These two sense organs are shown in Figs. .31 and 32. 

 Fig. 31 shows the under side of the head of Scutigera (Fig. 

 17), with the position of the sense organ and its opening. 

 Fig. 32 is part of a section through the head of Polyxenus with 

 two of the sense hairs. Each spine or sense hair fits into a cup 

 in the chitin of the head ; and the lower or internal part, which 

 is divided from the upper or external part by a rim, is joined to 

 a ganglionic nerve cell {gang.c). 



The Myriapods are of separate sexes, and the generative 

 organs in both cases usually have the form of a long unpaired 



