No. 393-.] REVIEWS OF RECENT LITERATURE. 743 
after careful examination have been generally admitted to be non- 
nucleated. Within the last year or so Petrone has succeeded in 
demonstrating, by means of improved methods of fixing and staining, 
that the adult mammalian corpuscle contains a differentiated body 
which he believes to be the remains of a nucleus. This body has 
been the subject of a careful study by Negri,’ who has satisfactorily 
identified it in the adult blood corpuscles of mammals, and who 
has also seen it in the blood of embryonic rabbits, where it exists in 
addition to the nucleus, thus showing that it is not to be regarded as 
the remains of an original nucleus. GHP. 
Development of the Teeth in Rodents. — The development of the 
teeth in rodents, as worked out by P. Adloff,? shows that the ances- 
tors of these mammals possessed a more nearly complete dentition 
than do the present forms. Many species show the rudiment of a 
first incisor which eventually disappears, the characteristic incisor 
of the rodent being the second, as compared with the dentition of 
other mammals. This homology was previously declared by Cope, 
on paleontological grounds, and now receives support from the em- 
bryological side. In the upper jaws of some forms, as, for instance, 
Sciurus, a rudimentary canine was found, while in the corresponding 
region of the lower jaw not even a dental ridge was observed. The 
lower jaw may sometimes show evidence of prelacteal germs, thus 
marking the rodents as forms in which three generations of teeth 
once occurred.. The paper is concluded with a short discussion of 
the question as to which generation the rodent molars belong. 
GR PF. 
Breeding Habits of Ornithorhynchus. — Notwithstanding the 
efforts which have been made within very recent years to ascertain 
the breeding habits of Ornithorhynchus, very little in reality is 
known. W. H. Caldwell, in his search for the eggs and young of this 
animal, found one female that had laid her first egg and had the 
second still in the oviduct; R. Semon was altogether unsuccessful in 
obtaining further observations. In view of this lack of information, 
the field notes of A. Topič, as communicated by Professor V. Sixta,” 
1 Negri, Ueber die Persistenz des Kernes in den roten Blutkörperchen 
erwachsener y ewed Anat. Anzeiger, Bd. xvi, pp. 33-38, 1899. 
2 Adloff, Zur Entwickelungsgeschichte des Nagetiergebisses, /enaische 
Zeitschrift, Bad. xxxii, pp. 348-410, Taf. xii-xvi, 1898. 
Wie junge rukke die Milch ihrer Mutter saugen, Zool. 
Anzeiger, Bd. xxii, pp. 241-246. June 12, 1899. 
