ZOOLOGY AND BOTANY, MICKOSCOPY, ETC, 235 



Of tlie Lepidoptera the author has examined 118 species (adult) 

 and 42 caterpillars. There are always two cephalic ganglia, and the 

 sub-oesophageal is convoluted. In most there are two distinct thoracic 

 masses ; sometimes (as in Cossus ligniperda, &c.) there are three. 

 There are always four abdominal ganglia, save in Hepialus Jiumuli, 

 which has five. 



The Diptera have always two cephalic ganglia, which are separated 

 from one another and connected by short commissures, and here again 

 the sub-cesophageal ganglion is always convoluted ; there is frequently 

 only one thoracic ganglion. There are one to eight abdominal gan- 

 glia, but these may be altogether fused with the thoracic. Pulex 

 cards has eight in one sex and seven in the other, and the same seems 

 to be true of P. irritans. The Diptera have a frontal, and two pairs 

 of small pharyngeal ganglia, but the abdominal part of the sympa- 

 thetic system is not distinct. 



Seventy species of Hemiptera have been studied, with the following 

 results : — In some the sub-oesophageal ganglion is fused with those of 

 the thorax ; in others, though distinct; it is placed in the thorax and 

 not in the head. The cerebroid lobes are always convoluted. There 

 are three thoracic ganglia in Pediculus, but as there are no commis- 

 sures, they touch one another. The Hemiptera appear never to have 

 any distinct abdominal ganglia, these being in all cases fused with 

 the thoracic portion of the nervous system. 



Sensory Nerve-endings in Skin of Insects.* — These have now been 

 found even in places where hairs, bristles, and all other special 

 cuticular formations are absent. H. Villianes has examined the skin 

 of Musca and Eristalis ; he finds the external cuticle to be thick and 

 devoid of the canals which so often occur in it in insects ; the hypo- 

 dermis immediately underlying it is composed of flattened hexagonal 

 cells ; a third layer consists of an amorphous connective membrane 

 containing round nuclei at wide intervals. Between this last layer 

 and the hypodermis lie irregular tracts of angular cells, from whose 

 corner proceed filiform processes, which are attached, some to the one, 

 some to the other of the two investing layers, by a triangular flattened 

 disk ; the cells are invested by a membrane and contain a round 

 nucleus ; the protoplasm does not penetrate into their angles ; they 

 become charged with fatty granules towards the end of larval life. 



By treating the skin with osmic acid the nervous fibres and cells 

 are demonstrated. The method is to treat the dermo-muscular coat 

 with 1 per cent, osmic acid, and then for ten minutes with 25 per cent, 

 formic acid ; it is then left twenty-four hours in J^ P^i" cent, chloride 

 of gold solution in the dark ; the tissue is finally exposed to the light 

 in a 25 per cent, solution of formic acid. When the cuticle is 

 removed, a great number of nerve-fibres without Henle's sheath 

 appear between the hypodermis and connective layer ; they branch, 

 anastomose, and swell out into a great number of multipolar ganglionic 

 cells, of an average diameter of "04 mm., and with four or five pro- 

 cesses as a rule, of which one, the " centripetal prolongation," is larger 



* Comptes Eendus, xci. (1880) pp. 1089-91. 



