PHYSIOLOGY OF THE INVERTEBRATA. 355 



The Myriapoda. 



Concerning the sense of touch in these animals, there are 

 on the antenna3 and other appendages, filiform prolongations 

 — these transmit the effects of mechanical pressure, &c,, to 

 the nerves attached to these organs. 



Although some species of the Myriapoda are blind, the 

 majority have eyes ; and these organs are either simple or 

 compound eyes. Prof. H. Grenacher has recently investi- 

 gated the eyes in this Arthropod class. He distinguishes 

 those of (i) ScolojMndnda:, (2) Lithohius, (3) Jidvs, (4) 

 G/omcris, and (5) Sfi'tifjcra; all except the last are stemmata. 

 Scutigera has compound eyes of a very anomalous type, in no 

 wise resembling those of the Insecta and Crustacea. The 

 eyes of the Chilopoda are more polymorphic and more com- 

 plex than those of the C/rUognatha {Diplopoda). Physiologi- 

 cally, the simple eyes of at least some of the Myriapoda must 

 be very unlike the ordinary stemmata of spiders or insects. 

 These are true eyes. In the Myriapoda., on the other hand, 

 each stemma has its retinal elements, or their representatives 

 so disposed in regard to the axis of the cornea-lens, and there- 

 fore to the incident rays of light, that it seems very doubtful 

 whether such eyes can do more than distinguish between 

 desrrees of ligrht and darkness. 



The sense of smell appears to be feebly developed in the 

 Myria^joda. 



The Insecta. 



" The sense of touch appears to be seated in the Insecta in 

 very different parts of the body. It is chiefly located in the 

 palpi of the mouth, which, for this purpose, are usually 

 terminated by a soft surface. The antennae also serve as tactile 

 organs, but in a very variable manner, according to tlu^ir 

 forms, the degree of their development, and the habits of the 

 species. These organs receive, each, directly from the cerebral 

 ganglion, a nerve ; these nerves perceive the slightest dis- 



