592 The American Naturalist. [June, 
4. The anterior part of one larva may be united to the posterior 
part of another individual. 
When the pieces are long, the same region is repeated in the result- 
ing fusion, since it is present in the posterior part of one larva and in 
the anterior part of the other. In only one case, however, did this ex- 
periment succeed. After five days there had been much growth, but 
the intestine had not fused across the line of union and there was no 
circulation in the posterior piece. 
5. Two frog larvee may be easily united belly to belly so that a true 
twin is formed. 
The animals may be united with the ends reversed as well as with 
the heads and tails in the same direction. 
6. It is even possible to unite larve of different genera even of dif- 
ferent families. 
. The posterior end of a frog larva was fused to the anterior end of a 
triton larva. : 
The anterior end of a frog larva and the posterior end of a toad larva 
(Bombinator igneus) were readily united. The inverse of this last ex- 
periment also succeeded. 
7. The larve of Rana esculenta and Bombinator igneus were united 
belly to belly, producing a true double monster, gastrophagus, made 
up of animals of two different genera. 
The Embryo of the Duckbill.—At the meeting of the Linnean 
Society of New South Wales, Nov. 28, 1894, J. P. Hill and C. J. Mar- 
tin read a description of an embryo of the duckbill taken from an in- 
trauterine egg. The embryo described was taken from one of two eggs 
just ready to be laid. The egg measured 18 mm. by 13.5, being some- 
what larger than the eggs described by Caldwell. The embryo was 
found lying on the surface of a thin-walled vesicle with its long axis 
corresponding to the long axis of the egg. 
It measured 19 mm. in length from the anterior end of the medullary 
plate to the posterior end of the primitive streak. The vesicle on 
which the embryo lay consisted of two layers all over, with the meso-- 
derm extending about half way round between and comparable to a 
typical mammalian blastodermic vesicle. The vesicle filled the whole 
of the egg, and contained a thin albuminous fluid together with a thin 
layer of yolk spheres next toits wall. The embryo with the exception 
of a slight head fold, is quite flat. Medullary folds are absent except 
in the most anterior region of the future fore-brain, where slight lateral 
upgrowths of the medullary plate appear. The three cerebral vesicles 
