340 E. T, NEWTON. 



of the external eplblast towards the hypoblastic outgrowtTrs 

 of the pharynx may occur, and that it is still a matter of 

 uncertainty whether some of the gills are not epiblastic 

 rather than hypoblastic ;^ while, if the diverticula of the 

 alimentary canal described above in the trout and salmon 

 should prove to be hypoblastic, the principal differences 

 between the olfactory organs and the gill clefts would be the 

 gradual shrinking of the most anterior pair of diverticula of 

 the buccal cavity, the ultimate failure on their part to reach 

 the surface, and a corresponding exaggeration of the epi- 

 blastic surface involutions, which changes can readily be con- 

 ceived as following on, and caused by, a slight displacement 

 backwards of the mouth. Since the functional activity of 

 the gills as such depends on the constant passage of a stream 

 of water through the mouth into the buccal cavity and then 

 out through the gill slits, it follows that if the mouth were 

 changed in position so as to be situated behind instead of 

 in front of, the first pair of gills, the function of these gills 

 would be materially interfered with, while their position at 

 the anterior extremity of the head and their consequent 

 potential utility, would favour their preservation in a modified 

 form, and with modified function. 



On the Brain of the Cockroach, Blatta ortentalis. By 

 E. T. Newton, F.G.8., H. M. Geological Survey. With 

 Plates XV and XVI. 



The common cockroach, Blatta ortentalis, has been found 

 a very convenient insect to take as a type of its order, both 

 on account of its generalised structure, and the readiness with 

 which it may be obtained, in any numbers, at all seasons of 

 the year; consequently it has been dissected largely in our 

 biological schools. 



It seemed desirable, therefore, when the structure of the 

 brain of certain insects was being investigated by several 

 continental naturalists, that we should make ourselves some- 

 what better acquainted with the brain of our typical insect 

 the cockroach, for this had not been worked out as care- 

 fully as it merited. And further, inasmuch as in certain 

 particulars this insect is less specialised than some of 

 those, the brains of which have been examined, it seemed 



' Balfour, op. cit., pp. 210, 211. 



