HARDWICKE' S SCIENCE-GOSSIP. 



59 



history of the extinction of a large bird in modern 

 times, and also possessing a good account of its habits 

 when still existing, I write these lines. Some time in 

 1S65, I think, Mr. E. Newton, then of the civil 

 service of Mauritius, sent some men to Rodrigues to 

 collect bones, all they could find, as no one acquainted 

 with osteology could get away. They were sent to 

 me to sort, as I then had plenty of spare time, and he 

 could come down at any odd chance to see how all 

 was going on. In a broad, upstairs-verandah, I 

 rigged up a table of planks on trestles, and weeded 

 out the greater number, being those of the large 

 tortoise, besides a number of bones of some small 

 birds, the remaining bones were undoubtedly those 

 of a large bird ; but some six or seven pinion bones 

 struck me as peculiar from a small round ball of bone 

 in them, the first two or three I took to be mere bits 

 of coral debris, &c., but here all were at the same part 

 of the bone ! Mr. Newton came and looked at them, 

 turned to Leguat's book, and read his description of 

 the birds when alive, and especially when fighting, 

 that they struck with their wings beneath which was 

 a lump of bone of the size of a musket ball ; so wrote 

 Count Leguat, and fortunate it was that he was a keen 

 observer and good describer, and that, under circum- 

 stances of much misery. 



{To he coiitinitcd.) 



FROG SPAWN AND ITS DEVELOPMENT. 



By M. H. RoBSON, Hon. Sec. North of England 

 jNIicroscopical Society. 



THE season is now near when the interesting 

 experiment detailed in the following paper can 

 be repeated ; it is one which can be carried out by 

 almost any person willing to bestow a little care and 

 attention daily for a few weeks. 



Little difficulty exists in obtaining frog sjoawn ; 

 usually it is within easy reach, being frequently 

 deposited at the shallow margins of ponds or ditches, 

 where it may be seen floating in gelatinous masses 

 during the early spring months. 



A dozen or so of the ova are amply sufficient for 

 the purpose of maturing : these are readily separated 

 from the mass in which there may be some hundreds. 

 Each ovum forms a central speck of inky blackness, 

 •['5 inch in diameter, in a transparent albuminous 

 globule, having a diameter of nearly half an inch ; 

 the whole is invested in a delicate membrane attached 

 to the general mass (fig. 49). 



The spawn intended for observation should be 

 placed in a shallow vessel containing water, and 

 covered with glass to exclude dust, having previously 

 put in a liberal supply of aquatic plants , preferably 

 callitriche, millfoil, chara, or nitella, as being most 

 likely to afford the tadpoles a sufficiency of Infusoria, 

 upon which they seem to subsist to a considerable 



extent after devouring the gelatinous egg mass which 

 appears to form their first food. They are thorou"-li 

 scavengers, and any decaying matter, either animal or 

 vegetable, is eagerly eaten. In confinement, however, 

 nothing putried must be permitted to pollute the 

 water in which the tadpoles are kept, otherwise they 

 soon die. The live tadpoles do not suffer their de- 

 funct relatives to be altogether lost, but, as cannibals, 

 speedily utilise tliem. 



On March 3rd, 1878, 1 procured a supply of freshly- 

 laid spawn ; this was very early in the year ; but 

 the weather had been open and mild for some weeks 

 before, and this day was singularly warm and spring- 

 like, vegetation was quite a month in advance of the 

 average season, and the batrachians moved actively in 

 the shallow pools. The vessels intended to receive the 

 spawn were placed in the window of a room having 

 a north-east aspect, and without a fire, the blinds 

 were kept undrawn, in order to imitate natural 

 conditions as closely as possible with reference to 

 temperature and light. 



Tlie freshly-gathered ovum when crushed between 

 two slips of glass and examined in water under 

 a quarter-inch objective is seen to be composed 

 of irregularly-shaped granules enclosed in a delicate 

 integument which, on being ruptured, lay in folds 

 amongst the corpuscles, these varied in size as in 

 shape, the larger granules measured jjL inch in 

 diameter with the suspicion of a nucleus. 



In appearance the ova changed little until the fifth 

 day, but the integument gradually thickened and 

 became so tough that it was now necessary to cut it 

 open in order to liberate the contents of the ovum. 

 These had become aggregated into small spherical 

 masses, the granules evidently nucleated, and from the 

 currents perceptible amongst them, it appeared that 

 ciliary action was in existence, although I could not 

 just then locate it. 



On this day also a cleavage or segmentation of the 

 ovum was observed, as in fig. 45, and the interesting 

 fact became apparent that the embryo frog, unlike 

 birds, or the mammalia, does not originate in a 

 single vesicle or sac on the surface of the yelk, but 

 in common with toads, newts, and some other 

 reptiles, the whole substance of the yelk becomes 

 transformed or moulded into the nascent tadpole. 



Figures 46 and 47 show the progress of cleavage on 

 the sixth and eighth days respectively. On March 

 1 2th, this being the ninth day from the deposition of 

 the spawn, a striking change was manifest ; the 

 embryo had assumed the form shown in fig. 48, where 

 A represents the natural size of ovum, as in pre- 

 ceding figures, and B the same magnified four 

 diameters ; at a are the rudimentary external gills ; the 

 inner circlet b surrounding the embryo is the vitelline 

 sac or zona pellucida, itself an object of singular 

 tenuity and crystalline transparency ; and at c is the 

 protruding tail. 



A change was now perceptible daily ; the gills and 



