Characteristics of the Vertehrata. Ixv 



the ducts of the Wolffian body form by fusion with each other a 

 secondary duet, which opens into the primitive duct of Miiller 

 at its lower end, leaving- the upper portion of that duct to serve 

 exclusively as a generative canal. 



The cerebral hemispheres always contain a lateral ventricle, which 

 is prolonged into the interior of the sessile olfactory lobes. The 

 optic lobes are smaller relatively than in Fish, in correlation with 

 the smaller eyes ; the optic thalami are always differentiated from 

 them, and from the corpora striata in front. The membranes of 

 the brain and spinal cord have an abundance of pigment cells in 

 their visceral laminae, and upon the exterior of these membranes, 

 and especially upon their prolongations upon the spinal nerves, 

 deposits of crystalline carbonate of calcium are commonly observ- 

 able. As in many Fishes^ the portio dura often fails to be entirely 

 differentiated from the fifth pair of nerves ; as in Lepidosiren, the 

 glossopharyngeal is represented by branches of the vagus, and the 

 hypoglossus by the first spinal nerve. The eye is small in com- 

 parison with that of Fish, but as in that Class the lens is sphe- 

 roidal, and the cornea, except in the Land Salamander, flat. There 

 is no tympanic cavity except in the Anura, and no cochlea except 

 in a rudimentary condition in the same order. In the aglossal 

 Anura {Pipa, Bacti/lethm), there is a single median pharyngeal 

 orifice to the two Eustachian tubes. The two nasal cavities open 

 into the mouth by a canal passing between the bones of the roof 

 of the mouth in Anura, but between those bones and the lips in 

 Perenn ibra n cli lata. 



Rudiments of an ovary have been observed to coexist with the 

 testes in the male Bufo variabilis and cinereus. The sexes are very 

 frequently distinguishable by external differences of colour, size, 

 and conformation, but there are no external copulatory organs in 

 this Class. The ova and spermatozoa come into relation with each 

 other externally to the maternal organism, but by means of 

 congress between the two sexes in the Anura; they come into 

 relation with each either externally to, or within the maternal 

 organism in the Urodela, and probably also in the Perennibran- 

 cJdata, but without, at least in the aquatic species, any sexual 

 congress. The Land Salamanders appear to be, under certain 

 circumstances, such as those of the Alpine species living at points 

 of great elevation in the mountains, ovo-viviparous or viviparous, 



e 



