138 SUMMARY OF CURRENT RESEARCHES RELATING TO 



around, the fibrous notochordal-sbeatb, and the notochord atrophies 

 early, playiug little part in the formation of a vertebra. In Teleostei 

 (Gasterosteus, Leptocephalus, Cyclopterus, &c), the vertebra developes out- 

 side tbe notochordal-sheaths, exclusively at the expense of the cells 

 of the perichordal connective-tissue. The cartilaginous arch-bases are- 

 in the majority of cases passive, whilst the notochord and its sheaths 

 are more important, especially in the inter-vertebral spaces. In short, 

 the vertebra of Teleostei is a specialised form of the vertebra of 

 Holostei. But this is only a suggestion of the author's main results. 



Ear-Bones of Opossum. * — E. Weil finds in a study of Dklelphys 

 murina confirmation of the conclusion that the malleus is a derivative of 

 the mandibular arch, and that the incus is likewise. The continuity of 

 incus and malleus is clear, and it is plain that the incus has absolutely 

 no relation with the hyoid arch. 



Two Hearts in a Pigeon. j — C. I. Constantinescu gives a descrip- 

 tion of a rare abnormality — two complete and normally formed four- 

 chamhered hearts in a pigeon. The larger was ventral, the smaller 

 dorsal; theie was no communication between them; there were abnor- 

 malities in the arterial trunks and veins, but the heart had been cut 

 out before the author got it. There must have been a complete duplicity 

 in the development of the primitive cardiac tubes. A few — somewhat 

 vaguely recorded — analogous cases are referred to. 



Origin of Lymphoid Elements of the Thymus in Teleosts. + — 

 Prof. J. Nusbaum and Th. Pryrnak find that in Salmo fario and Caras- 

 sius vulgaris large numbers of lymphoid elements ("lymphoid nuclei"), 

 which are to be observed in the earliest stages of the thymus, originate 

 from the (endodermic) ejnthelium of the pharyngeal mucous membrane 

 in the branchial region — a conclusion of importance. It seems to the 

 authors that this is the real source of the lymphoid elements of the 

 thymus. In later stages they also observed a marked migration of 

 leucocytes from the thymus into the surrounding tissue — a fact of im- 

 portance in connection with the functional role of the thymus in fishes, 

 and in accordance with Dr. Beard's results as to Selachians. 



Pseudobranch of Amia calva.§ — Mr. E. P. Allis has made a detailed 

 study of the pseudobranchial circulation in embryos of this Ganoid. 

 He finds that the nature of the blood-supply shows that the pseudo- 

 branch is the homologue of the spiracular clemibranch of Selachians. 

 There is some uncertainty as to whether it belongs to the mandibular or 

 the hyoidean arch, though the comparison with Selachians suggests the 

 former arch as the region of origin. 



b. Histology. 



Histological Study of Crystals. || — Pi of. 0. Biitschli has already 

 extended his detection of alveolar structure from cytoplasm, to sub- 



* Ann. New York Acad. Bci., xii. (1899-1900) pp. 103-7 (2 pis.). 

 t Hull. Soc. Sci. Bucarest, ix. (1900) pp. 403-5. 

 X Anat. Anzeig., xix. (1901) pp. 6-19 (-1 figs.). 

 § Zool. Jahrb., xiv. (1900) pp. 107-34 (1 pi). 



|| ' Unter&uchungen iiber Mikrostrukturen dcs erstarrten Fchwefels, etc.,' Leipzig,. 

 1900, 4to, 96 pp., 4 pis., 6 figs. Sec Amer. Nat., xxxiv. (1900) p. 976. 



