POUCHED RATS. 



271 



Richardson was slow to discard his original conception. In the zoology of Captain Beechey's 

 Voyage he repeats his belief that " the figure in the Linnean Transactions is a correct representation 

 of the fonn of the animal, and gives the true appearance of its cheek-pouches when distended w^th 

 food."* He in some way had become convinced that the cheek-pouches of both Geomys bursarius 

 the original culprit, and of Geomys Douglasii, opened internally, and were pendidous ; and he 

 described the Californian Gopher as a new genus, under the name of Diplostoma bulfivorum, 

 because he could not get the pouches to assimie this form. He tried to evert them, without success. 

 They would not become pendulous. " Its bottom alone can be turned out, by which it is emptied 

 of its contents in the manner mentioned by Mr. Schoolcraft : but the lining of the exterior parietes 

 of the pouch is firmly united to the external skin, and i.s incapable of being everted."t He forgot 

 that the knife of the taxidermist passed between the two would separate the folded skin easily 

 enough. 



Fig. 2 shows the true form of the month of the sj)ecies which gave rise to the mistake. From this 



Fig. la.— Hj-pothetical Sand Bat 

 (Geomys bursarius. ) 



Fig. 2.— Real S.and Rat (Geomys burs-arius) 



Fig. 14— Hypothetical Sand Rat 

 (Geomys biirsariiis.) 



we see that the mouth of these Geomyn^e is very pecidiar. It is a sort of double mouth — an outer hall 

 or porch, and an inner room : the outer hall is clothed with hair, like the rest of the body, the 

 hair extending behind the incisors, both above and below ; and it is in the side-walls of what 

 are really its ^vide lips that the pouch occurs. "NYliat is called the mouth only commences at the 

 molars, and the entrance to it is very small, as the entrance to the other is very wide. The 

 incisors have a most • pecidiar look, thus standing isolated in the midst of the hairy face; but 

 there is nothing unnatural in it. There is no physiological reason why hairs should not grow 

 on the mucous membrane of the mouth, as well as on the skin of the face or body. The one 

 is a mere continuation of the other, and we see it grow in the mouth in some animals. The 

 whale grows its moustache inside its mouth instead of outside. The llhytina grew it in its palate ; 

 whalebone, horn, and hair being all diflercnt forms of the same thing. It therefore appears that 

 the term, external cheek-pouches, is a misnomer ; although apparently external, they are, in reality, 

 internal, and situated in quite the same homological position as those of the Hamster. The idea of 



* Beechey's " Voyage, Zoolog." p. 9. 



t Richardson, op. cit. 



