ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
59* 
the same genus, the great majority (62) have resulted in sterile offspring. 
In about 12 cases, the offspring have been fertile with one of the parent- 
species or with a third species ; in seven or eight cases they have proved 
fertile inter se, sometimes for three or four generations. 
Among birds, in 78 crosses between distinct species, but of the same 
genus, only 22 have resulted in fertile offspring, 8 inter se, the others 
with the parent species, or with a third species, or with other hybrids. 
Of the 68 crosses between species of different genera, but belonging 
to the same family, only one had offspring fertile with one of the parent 
species — the male hybrid of Columba livia x Turtur risorius was fertile 
with the female of the latter species. The female hybrid seems sterile. 
In two other cases a hybrid of this category fertilised a third species ; in 
another case it was fertilised by this third species. 
(3) As to the causes of sterility, the gonads may be atrophied, the 
ducts may be abnormal, and so on ; there is no doubt that the defect is 
constitutional ; but little more can be said. 
Regeneration in Vertebrates.* — Herr Tornier has two preliminary 
notes on the production of supernumerary tails, limbs, and digits in Ver- 
tebrates after certain kinds of injury, whether artificial or natural. In 
lizards it is easy to obtain double or even triple regeneration of the tail 
by injuring two or three vertebras at once. When three tails are present, 
the whole three are not usually visible externally, but can be demon- 
strated by means of the Rontgen rays. By amputating a limb and tying 
a thread in the middle of the wound, it is possible to obtain a duplex 
regeneration. Similarly, by successive injuries it is possible to produce 
supernumerary limbs or digits. In the case of extra digits in Mammals, 
the additional ones are always images of the normal (cf. Bateson), so that 
the limb appears to consist of a combination of a right and left limb. 
Such supernumerary limbs or digits the author regards as the result of 
pressure on the amnion, causing this to grow out into folds, often sym- 
metrical, which press against the growing limbs, and stimulate these to 
regenerate the part injured. 
Von Baer’s Philosophy.! — Herr E. Wasmann briefly reviews Dr. R. 
Stolzle’s | new book on Von Baer. He praises its impartiality, and 
describes it as containing a full exposition of Von Baer’s views on 
biological and other problems. 
Variation of Fin-Rays of Fishes. § — Dr. Georg Duncker has made 
an extended series of observations on the correlation in the number of 
fin-rays in the different fins of Acerina cernua L. The observations were 
made in 1900 cases between the vertical fins and their respective seg- 
ments ; in 1650 cases between the pectoral fins ; in the same number 
between the pectoral fins on the one hand and the dermal rays and the 
total number of rays of dorsal and anal fins on the other. The results 
show that, in the case of vertical fins, there is negative correlation 
between the dissimilar segments, positive between the similar segments 
and the total number. Between the pectoral fins there is marked posi- 
* Zool. Anzeig., xx. (1897) pp. 356-61 ( 6 figs.), and pp. 362-65 (3 figs.). 
f Biol. Centralbl., xvii. (1897) pp. 799-800. 
t ‘ Karl Ernst v. Baer und seine Weltanschauung,’ by Dr. Rem. Stolzle, Regens- 
burg, 1897, 687 pp. § Biol. Centralbl., xvii. (1897) pp. 785-94, and 815-31. 
