BURRELL. 21 



The total results were thus: — One female with intra-uterine egg's, six nests 

 with egg or egg's, and five nests with young. The eggs were fixed by making a 

 small incision with a sharp scalpel in the shell and immersing whole in the 

 fixing fluid. The young were also fixed by total immersion, after a small incision 

 had been made in the ventral body wall. All the material, with the exception of 

 one paii- of eggs and a couple of young ones which I have kept as trophies, has 

 been handed to Professor Harrison, who writes me as follows: — 



"I must congratulate you upon your splendid achievement. No such im- 

 portant collection of embryological material of Oniithorhynchus has ever been 

 got together before, and only a man with your intimate knowledge of the habits 

 of this interesting animal could have hoped to obtain so much in a single season. 

 Caldwell obtained eggs in 1884, but I cannot find that their contents were ever 

 described. Kershaw also obtained eggs, but these, again, were not, as far as I 

 am aware, opened. Wilson and Hill have obtained a number of intra-uterine 

 eggs, which they have fully described, but have not dealt with any embryos from 

 eggs from the nest. Parker, Poulton, and Wilson have all figured early young, 

 the mammary foetus, as Wilson calls it, but these are considerably more advanced 

 than the oldest of the series you have handed me. You may imagine the interest 

 with which .Mr. Briggs and myself have opened up the cheese-cloth and cotton 

 wool surrounding the specimens. The opening of the eggs was a ticklish business. 

 We had no idea how the embryo lay within the egg, and were both loth to take 

 I he first step, for fear of injuring so precious a specimen. Finally I sent Mr. 

 Briggs out of the laboratory, determined, if I made a hash of it, to have no wit- 

 ness to my shame. 1 was very relieved, on enlarging your careful incision to a 

 small window, to see a beautifully pi'eserved embryo on the opposite wall of the 

 egg. After that the rest was easy, and we have five nicely graded stages from 

 the egg, as well as four graded mammary foetus, nine stages between the oldest 

 intra-uterine embryo described by Wilson and Hill and the youngest mammary 

 foetus hitherto dealt with. The preservation is admirable, and not a single speci- 

 men is injured in any way. We are quite at a loss how adequately to give ex- 

 pression to our gratitude to yon for the privilege of examining this interesting 

 and important series ofembryos." 



The collection and preservation of this embryological material was, of course, 

 incidental to my own studies on the bionomics of the platypus. It is very grati- 

 fying to me, however, to find that I have been able to render a valuable service 

 to another branch of biological science, and that the years which I have devoted to 

 the study of Omithorhynchus have not been spent in vain. 



As will be seen from the list given above, the number of eggs varies from one 

 to three. I have now found one egg, or one young one, sufficiently often to be 

 quite sure that one is frequently the normal complement. Two other pieces of 

 evidence put this quite beyond doubt. In the first place, dissection of a female 

 captured in a nest containing one egg only showed no trace of another egg in 

 either uterus ; while, where two or more eggs are laid, these are always firmly 

 adherent one to another , and I believe that this adhesion takes place prior to 

 laying. I have found one egg, or one young, in six out of seventeen tenanted 

 nests examined during the past three seasons. 



Eleven of these nests contained twin eggs or twin young, so two would appear 

 to be the normal number. The twin eggs are attached to one another with their 

 long axes sub-parallel, and Professor Harrison tells me he had to exercise con- 

 siderable force to pull the adherent walls apart. Of four pairs of twin eggs, in 

 one_only were the eggs equal in size (Plate II., Fig. 3), there being a difference of 



