IOWA ACADKMY OF SCIENCES. 



127 



meters. Lateral (throujth base of cerebral hemispheres) seventeen millime- 

 ters. Dorsoventral (throuprh median commisure), eleven millimeters, the 

 largest 30x20x14 mm. The average weight of nine brains is three and tive- 

 tenths grams, the heaviest 3.'J23, lightest, 2.3013. 



On the dorsal aspect of the pons at the end of the fourth ventricle is a 

 curtain like aflfair at right angles to the longitudinal dimension of the ven- 

 tricle called the valve of Vieussens. In G. burscums this portion is very 

 small. It appears to be attached to the anterior crura of the cerebellum. 

 Anterior to this valve of Vieussens are two bodies, each deeply cleft or lobed 

 into two hemispheres. They correspond to the Corpora quadrigemina of 

 higher animals. The anterior body miglit be termed the tubercular nates, 

 the posterior the tubercular testes. Still more anteriorally situated are two 

 masses which are longer comparatively in G. bursarius than in either S. tri- 

 decemlineains, or L. cunictdus. They are the Thalami optici. :»: # * 



The cerebellum is rather spheroidal in shape, aud in mass compares with 

 the cerebrum as about one to four. In the higher animals this portion of 

 the eucephalon is divided into two distinct hemispheres, each hemisphere 

 being in turn cleft into several lobes. But in G. biorsaruis it is:more accu- 

 rate to consider it as composed of three distinct lobes, called respectively, 

 the central lobe and the two lateral lobes. Just lateral to these parts, on 

 either side, is a peculiar body coiled upon itself, somewhat like a snail shell, 

 called the Flocculus. * » * 



The surface shows a sort of convolution being traversed in a general 

 transverse direction by numerous curved furrows or sulci, which vary in 

 depth in different parts, in this respect the cerebellum is quite similar to 

 that of higher forms, which is also true of its structui'e and the arrangement 

 of the gray and white matter which on cross section shows the character- 

 istic arbor vitaj appearance. 



On thvi ventral surface of the cerebrum, extending well forward from 

 about the center of each hemisphere, are the olfactory lobes; they protrude 

 about two to four millimeters beyond the frontal lobes. 



The eighth pair, or auditory nerves, are large comparatively, and origi- 

 nate in a groove between the olivary body and restiform bodies at the pos- 

 terior border of the pons. 



The earthworms of the State wei-e studied by Miss Vinnie Williams of 

 class of 1893. with the result of finding, according to her determination, tvo 

 distinct species in the State. 



These were the Allolobophora turgida, specimens of which were secured 

 from Tama county, and the Ltanbricus rubellus, species of which were 

 obtained from Chickasaw and Powesliiek counties. 



Doubtless other species occur, but apparently no one has hitherto 

 recorded any determinations. The species most common at Ames is prol)- 

 ably the Allolobophora ttirgidn, but with ordinary preparation the positive 

 separation of species is difficult aud few have been examined when prepared 

 so as to permit rigid examination. 



