ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 401 



Ovary of Echidna.* — Dr. G. A. Guldberg finds that during the 

 whole of its development the ovarian egg completely fills the ovarian 

 follicle, and is only surrounded by a unilaminate layer of follicular 

 epithelium ; this, later on, forms a permanent investment round the 

 egg, and is distinguishable from all known forms of eggs in other 

 orders of mammals. During development the protoplasm of the egg 

 undergoes a difierentiation into small and larger yolk-spheres ; then 

 increases in size until at last only a small part of the less difteren- 

 tiated protoplasm surrounds the peripherally placed nucleus. Two 

 poles can then be distinguished in the egg, one the nuclear, and the 

 other the vitelline. The egg is generally at least 2-5 mm. in 

 diameter before it leaves the ovary, and it may be as much as 3 mm. 

 The ovarian membrane then chiefly consists of a " chorion," which is 

 formed by the follicular epithelium. The nucleus is distinguished 

 not only by its size, but also by the number of smaller paranuclear 

 spots. 



The observations of Dr. Guldberg show that the egg of the 

 Echidna approaches in many points to the Sauropsidan type, and 

 the view of Poulton that we have here to do with unequal segmenta- 

 tion appears to be correct. 



Monstrosities with Double-hearts. f — M. S. Warynski records 

 various experiments, undertaken by himself and Prof. H. Fol, on the 

 production artificially of double hearts in chicks, and gives a resume 

 of the various works on the development of the heart from Pander, 

 1817, to Kolliker, and Hensen in 1876. 



The union of the pair of " cardiac blastemas " takes place about 

 the thirty- sixth hour of incubation ; and it was between the twenty- 

 fourth and thirty-sixth hour that the author's experiments were made. 

 While the earlier authors, holding the idea that the heart was formed 

 from a single "blastema," considered that a double heart was pro- 

 duced by the subsequent division of the organ, the later observers, 

 finding the double origin, explain the monstrosity by a non-union of 

 the two halves, owing to some arrest in normal development. The 

 cause of this arrest or interference was unknown. 



This form of monstrosity ordinarily has some other abnormality 

 associated with it, so that the embryo usually dies before being 

 hatched ; but the author was able to produce a double heart in a chick, 

 which was otherwise normal. The mode of procedure is as follows : — 

 The blunt edge of a scalpel is carefully and lightly drawn backwards 

 along an embryo, between twenty-four and thirty-six hours old, from 

 just behind the head, without injuring any tissues ; the duration and 

 force of the pressure must be carefully regulated, as otherwise the 

 embryo will present various abnormalities. If all goes well, the 

 embryo will continue to develope normally, with the exception of 

 possessing two hearts. 



But this normal development is very exceptional, as the duality 

 of the heart is usually accompanied by some such abnormality as 



* Jenaisch. Zeitaclir. f. Naturwiss., xix. (1885) Supp. ii., pp. 113-22 (1 pi.) 

 t Eecueil Zoul. Suisse, iii. (18S6) pp. 261-311 (1 pi.). 



