894 DR. W. E. AGAR ON THE NESTING-HABITS [Dec. 14, 



emptij gelatinous egg-capsules, forming together a stiff jelly. 

 These egg-capsules are of coui'se seci'etions of the oviduct. They 

 are little solid spheres of jelly, made polygonal by mutual pressure, 

 and except that they are a little smaller are exactly like the capsules 

 laid later and containing eggs. 



As the act of oviposition continues, egg-containing capsules 

 begin to appear among the eggless ones, and the bulk of the 

 nest is filled with a, mixture of full and empty capsules in about 

 equal numbers. Finally, as oviposition approaches its end, the 

 egg-containing capsules become fewer and fewer, and the last 

 addition to the nest is a mass of empty capsules as at the beginning 

 of the process.* 



In oi-der to confirm this view as to the way in which the mass 

 of spawn is made up, which was deduced from examination of a 

 number of nests, I made a dissection of a frog which I had preserved 

 in the act of oviposition, when the nest was about half filled. 

 The dissection (PI. LXXXIV. tig. 2) shows precisely the conditions 

 to be expected from the structure of the nests. Each ovisac con- 

 tains a mass of encapsuled eggs and empt}^ (i. e. eggless but solid) 

 capsules. The former occujoy the postero-ventral and the latter 

 the antero-dorsal portion of the ovisac, but the line of demarcation 

 between the two is not precise. A glance at the figure will show 

 that at the moment when the frog was preserved (in the middle of 

 oviposition) it was laying a mixture of full and empty capsules, 

 but as oviposition continued the proportion of full to empty ones 

 would become less and less, and finally it would be laying empty 

 ones only. The contents of the ovisac of the other side are 

 a,rra,nged in a precisely similar way. 



The mass of spawn when finished is thus largely, or often even 

 mainly, made up of empty capsules. The egg- containing capsules 

 are embedded in the mass in such a way that in well mqde nests, 

 such as the one figured, not a single e^g is exposed to the light 

 and air, the jelly plug of empty capsules at the top and bottom, 

 and the leaves at the sides forming a complete shield for them. 



Each egg is of course enclosed in a vitelline membrane as well 

 as the gelatinous oviducal envelope. As the time for hatching 

 approaches a large quantity of fluid accumulates inside the vitelline 

 membranes, causing them to swell up to twice their proper size 

 and giving the embryos room to make violent movements within 

 the membranes and to give free play to their large external gills, 

 which may be seen moving to and fro. 



The fluid inside the vitelline membranes has evidently been 

 extracted from the jelly of the oviducal enveloj)es, both of those 

 surrounding eggs and of the empty, solid ones; for whereas in 

 the newly laid egg-mass each vitelline membrane fits close I'ound 

 its egg, and is separated from its neighbours both by its own and 

 their own thick oviducal capsules, and also by the empty capsules 



* 111 the figure some of the leaves have been turned aside to expose the egg-mass. 

 Ill its natural condition none of the eggs were visible, only the mass of empty 

 capsules at the top and bottom being exposed. 



