ZOOLOGY AND BOTANYj MICROSCOPY, ETC. 349 



It is impossible to produce offspring by tbe union of the male 

 and female products of two different Batracliian ppecies, though seg- 

 mentation of the egg, frequently of abnormal type, may be started by 

 this artificial union. 



Sense of Direction in Animals.* — The remarkable faculty which 

 cats, dogs, pigeons, and other animals possess, of returning in a 

 straight line to a point of departure, has awakened much curiosity on 

 the part of naturalists. Some refer it to instinct, some to intelligence 

 similar to that of man, some to an internal mechanism which makes 

 the animals simply automata ; but none of these attempted explana- 

 tions do anything towards solving the mystery. Wallace supposed 

 that when an animal is carried to a great distance in a basket, its 

 fright makes it very attentive to the different odours which it 

 encounters upon the way, and that the return of these odours, in 

 inverse order, furnishes the needful guide, Toussenel supposes that 

 birds recognize the north as the cold quarter, the south as the warm, 

 the east (in France) as the dry, and the west as the moist. Viguier, 

 in the ' Eevue Philosophique,' publishes an original memoir upon the 

 sense of orientation and its organs, in which he attributes the faculty 

 to a perception of magnetic currents. 



Cerebral Homologies in Vertebrates and Invertebrates.f — In 

 this very interesting contribution Prof. Owen distinguishes between 

 the neurcBsophageal and the heemoesophageal aspects of an animal's 

 body ; and speaks of the side of the body of a cuttle-fish denoted 

 by the neuroesophageal (" suboesophageal " so-called) brain-part, with 

 the chief nervous extensions therefrom along the trunk, as the 

 " neural aspect," and the opposite side to which the hsemoesopha- 

 geal (" supra-oesophageal ") brain-part has been turned by the course 

 of the gullet, as the "haemal aspect." What is usually called the 

 upper surface in Invertebrates is the " htemal " one, and the lower 

 the " neural " one. So the heart in man indicates the " haemal " 

 aspect, the myelon the " neural " part of his body, as in the animals 

 below him whether vertebrate or invertebrate. 



Attention is directed to the fact that in Invertebrates there is not 

 the same concentration of sensory organs as in Vertebrates, an 1 that 

 among the latter themselves we find (e. g. Cyprinoids) the olfactory 

 separated by long cords from the optic ganglia. The '* subcesophageal 

 ganglion " is regarded as the homologue of the medulla oblongata, or 

 " so much of that myelencephalous tract as may be in connection 

 with the trigeminal and hypoglossal nerves," or, in other words, with 

 the part that affects the vertebrate mouth. The ear in Orthoptera is 

 found in the first pair of legs. Basing himself on these and other 

 facts, the author concludes that " the collective neural centres and 

 their intercommunicating tracts in Invertebrates are the homologues 

 of those centres and tracts called ' brain and spinal cord ' in Verte- 

 brates, and that such 'neural axis' marks, in both grades of the 



* Chron. ludustr., Nov, 2, 1882. See Joura. Frankl. Institute, cxv. (1883) 

 p. 314. 



t Journ. Linn. Soc. (Zool.), xvii. (1883) pp. 1-13. 



