340 SUMMARY OF CURRENT RESEARCHES RELATING TO 



segregate in the F 2 generation are affected by the distribution of those 

 characters over the parentage and ancestry of the forms crossed. 



The results of the experiments prove : — 1. That the phenomena of 

 dominance, and, what is more important, of the segregation of characters 

 in definite proportions, are independent of the ancestry (and of the 

 geographical source) of the parent-forms mated. 2. That the recessive 

 character which reappears in F 5 is as pure as that borne by a pure race, 

 as tested by the results of its union with a pure dominant character. 

 3. That there is nothing like ancestral contributions within the limits of 

 a single unit-character. 4. That in the attempt to predict the result of 

 a given mating, the somatic characters not only of the parents and of 

 the ancestors of the individuals mated, but of the individuals them- 

 selves, may be entirely left out of account, aud that the expectation 

 based on a theory of the contents of the germ-cells of the two individuals 

 mated is fulfilled. 



b. Histolog-y. 



Structure of Dentine.* — V. v. Ebner finds that in typical normal 

 dentine there are, apart from a thin superficial layer under the enamel, 

 no oblique and radial fibres, i.e., fibres which do not cross the canaliculi 

 at right angles. The descriptions of oblique and radial fibres given by 

 v. Korff and Studnicka are due to misinterpretation. 



Smooth Muscles of Birds.f — A. Lelievre and E. Retterer have 

 studied the structure of smooth muscle in fowl and pigeon. The 

 sarcoplasm is traversed by a chromophilous reticulum ; the principal 

 trabecule are parallel to the long axis, but they are united by oblique 

 and transverse anastomoses. At the contact of two fibres there is a 

 thicker trabecula, which is limited laterally by sarcoplasm, or even 

 separated from the sides of the adjacent cells by a clear cytoplasm 

 traversed by fine branchlets. This cortical reticulum has been described 

 as intermuscular or interfibrillar connective tissue, as uniting bridges, 

 or as exoplasmic alveoli. But it is, according to the authors, of the 

 same nature as the intramuscular reticulum, the meshes containing 

 hyaloplasm instead of sarcoplasm. 



Lymphatic Ganglia in Birds.J — J. Jolly has examined twenty-five 

 species, and found ganglia on the cervical lymphatic only in web-footed 

 forms — duck, teal, goose, and swan. Usually there is a single ganglion 

 on the posterior surface of the jugular vein, below the level of the 

 thyroid. Sometimes there is a second lower down where the axillary 

 and thoracic lymphatics come in. Besides cervical ganglia there are on 

 each side of the aorta, between the origin of femoral and ischiac arteries, 

 at the confluence of lymphatics, small glandular masses which have a 

 ganglionic basis. A section of these various ganglia shows a network of 

 fine lymphoid trabeculas containing well-developed blood-vessels. In 

 the spongy tissue there are compact lymphoid mass (lymphatic nodules, 



* Anat. Anzeig., xxxiv. (1909) pp. 289-309 (9 figs.), 

 t C.R. Soc. Biol. Paris, lxvi. (1909) pp. 449-52. 

 X Tom. cit., pp. 499-502. 



