ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 251 



optic ganglion. Otherwise there is no difference as regards the brain 

 between the two sexes. 



The ocelli and the compound eyes are both connected with the pons 

 protocerebralis, which may be regarded as an optic centre. The 

 " central body " of the protocerebrum receives the dendrites of com- 

 missural fibres from all parts of the brain, and is in direct connexion 

 with the motor centres of the ventral chain of ganglia. A. comparison 

 of the brains of different insects shows that the degree of development 

 exhibited by the central body is in inverse.ratio to that of the mushroom- 

 shaped bodies. Bretschneider concludes that the central body is a 

 primary reflex- or association-centre, and the mushroom-shaped bodies a 

 secondary association-centre. The latter are the chief seats of the more 

 complex instincts and of memory. That the cockroach has memory is 

 proved experimentally. The innervation of the antennas is peculiar, 

 the first joint having special motor and sensory nerves which have a 

 complex course. The tritocerebrum and the deutorocerebrum consist of 

 cells and glomeruli. Besides the previously described tritocerebral 

 commissure there is a second which also contains motor fibres innervating 

 the oesophageal musculature. 



Tbe brain of Tenebrlo undergoes during the metamorphosis an 

 important increase in size and a change of shape and position. The 

 optic ganglion and the pons are almost entirely formed anew. There 

 is a notable increase in the size of the central body, the protocerebral 

 lobes, the deuterocerebrum, and the tritocerebrum. The mushroom- 

 shaped bodies remain almost unchanged. 



Bretschneider connects the post-embryonic development of the pons 

 and the central body with the new formation of the optic lobe, the pons 

 being regarded as an optic centre and the central body as a primary 

 reflex centre. The cell proliferation proceeds from special formative 

 centres. Two of these are very distinctly evident in the optic ganglion ; 

 one is to be clearly seen in the deuterocerebrum, and another in the 

 tritocerebrum. 



The mushroom-shaped bodies have no developed calices. They 

 represent a state intermediate between that of Lepisma and that of 

 Periplaneta. Characteristic of Tenebrio is the fine development of the 

 " parosmetic mass" which lies in the deuterocerebrum between the 

 trabecular of the mushroom-shaped body and the olfactory glomeruli. 

 The deuterocerebrum of the larva has to do with movement and nutrition, 

 but in the adult it has to do also with the finding of the other sex and of 

 a place for egg-laying. In the meal-beetle the pharyngeal nerve arises 

 from the protocerebrum. In the larva the labral nerve unites for a 

 certain distance with the mandibular. 



The mushroom-shaped bodies develop in insects from small beginninus 

 (in forms like Lepisma and Tomocerus) and become functionally the 

 most important part of the brain. As they increase the central body 

 decreases. Bretschneider recognizes six grades : (1) in Apterygota, the 

 central body is large and the mushroom-shaped bodies are primitive : 

 (2) in Hemiptera, Diptera, Libellulida?, the central body is large and the 

 mushroom-shaped bodies are unimportant ; (?>) in Coleoptera and lower 

 Hymenoptera, the central body is still large, but the mushroom-shaped 



