ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 249 



thickening of the muscular walls. This was specially apparent in the 

 fish-fed birds, though the intestinal surface was not the largest. The 

 weight and surface of the proventriculus increase in proportion to the 

 size of the prey. This is purely the result of a mechanical action and 

 was well shown by the fish-eaters. 



The chemical effects of the different diets were seen first in the liver, 

 which underwent profound modification. Fish-diet and insect-diet 

 caused hypertrophy, but both a pure flesh-diet and a vegetable-diet 

 caused a diminution in weight. The kidneys were modified in a 

 precisely similar way in relation to the different diets, and this seems to 

 the author to point to the greater toxicity of fish and insect as compared 

 with flesh and vegetable food, but further investigation would be 

 required to show whether some other organ, such as the skin, does not 

 react more to a purely flesh diet. The young ducks required more food 

 than the adults. A flesh-diet proves the best as regards growth, and 

 the best even in adult life, though less markedly so. Insects were 

 nearly as nutritive as beef during growth, but in adult life they proved 

 inferior. Fish and vegetables showed themselves unsuited for the 

 younger stages, but in adult life vegetables proved only slightly inferior 

 to beef. Laving began earliest and was most abundant in the fish-fed 

 birds. The modifications brought about in the ducks by each class of 

 diet correspond generally to the characters of the birds whose natural 

 food resembles that class, and the experiments therefore afford striking 

 proof of the great importance of diet as a factor — direct or indirect — 

 in evolution. 



Tunicata. 



Central Nervous System of Tunica nigra.*— W. A. Flitton de- 

 scribes the central nervous system of Tunica nigra. The ganglion of 

 this form possesses more branches than have been described for related 

 forms. Many of these branches are quite small, and seem to supply 

 the muscles near them. The neural gland on the ventral side of the 

 ganglion is in places almost fused with the nerve-centre, but free nerve- 

 cells were not found among the gland-cells. The duct from the gland 

 to the ciliated funnel was much like what has been described for other 

 forms. Small somewhat, variable strands were recognized in some 

 specimens as rapheal nerves. Another rather thicker mass of nervous 

 substance was found ending abruptly in connective tissue. None of 

 these peripheral nervous structures contained nerve-cells. The nerve- 

 cells of the ganglion were densely crowded into a cortical layer, the 

 central cone being "composed chiefly of nerve-fibres. There were a few 

 scattered cells in the central part of this mass of fibres. A large 

 proportion of the cells of the periphery evidently supply muscles. A 

 few cells of the peripheral portion of the ganglion, and many of the 

 scattered central cells, serve apparently for various kinds of associa- 

 tions. In all parts of the ganglion are cells which are apparently 

 connective rather than nervous in function. These are usually smaller 

 than the nerve-cells and have very little cytoplasm, for the central 



* Zool. Jahrb., xxxvii. (1913) pp. 113-30 (11 figs.). 



June 17th, 191 J P s- 



