OVUM. 



49 



In illustration of the most striking of these 

 differences of size in the ova of animals, the 

 following examples may be referred to : 

 The human ovum is a body not more than 

 a .i u - of an inch in diameter ; so minute, in fact, 

 that we can scarcely form any estimate of its 

 weight or quantity of matter. Let us assume, 

 what seems probable, that it weighs about 

 -j-J^j. of a grain. Now, if we take the weight 

 of a full-grown foetus as between six and 

 seven pounds, or 45,000 grains, and the adult 

 human body as about 120 or 130 Ibs., or 

 900,000 grains, it appears that while the full- 

 grown foetus bears the proportion of one- 

 twentieth of the weight of the adult, the ovum 

 is scarcely a thousand-millionth part. In the 

 fowl, the entire egg, when newly laid, weighs 

 about 2 ounces, or 900 grains, and is nearly 

 one twenty-second part of the weight of 

 the adult body, supposing it to be some- 

 what under 3 Ibs. The chick, produced 

 by incubation, is about 600 grains in weight, 

 or about two-thirds of the egg, and is, there- 

 fore, somewhat less than a thirtieth part of 

 the weight of the adult. Again, let us take 

 the weight of an osseous fish (as in a female 

 cyclopterus lurnpus recently measured by 

 myself), at 9 Ibs. 8 ounces, or 66,500 grains ; 

 one of the ova, which were fully developed 

 and filled two enormous ovaries, weighed one- 

 seventh of a grain ; and the foetus of such a 

 fish, when it first leaves the egg, might pro- 

 bably weigh not more than one-tenth of a 

 grain ;so that the egg would be in the propor- 

 tion of 1 to 500,000, as compared with the 

 body of the fish. 



It is to be observed, however, that this 

 great disparity of size belongs principally to 

 the nutritive part of the egg, and that there is 

 a nearer approach to uniformity in the size of 

 the germinal vesicle ; but in this, too, we shall 

 afterwards see that the size is greatest in the 

 ova of the second group, in which the whole 

 ovum attains the greatest magnitude. In the 

 mammiferous ovum, the germinal vesicle is 

 about -g-Q or ^i_ of an inch in diameter ; but 

 in the fowl's egg it is of a diameter about ten 

 times greater, and in cartilaginous fishes it is 

 even of a somewhat larger size ; but still in no 

 egg does this vesicle depart altogether from 

 that small and almost microscopic magnitude 

 which may be regarded as characteristic of 

 the elementary organic structures. 



The size of the ovary, when full of developed 

 ova, is also deserving of notice, as giving some 



over its long diameter, is stated to have been nearly 

 three feet, and over its short diameter two feet four 

 inches ; its greatest length nearly thirteen inches. 

 M. Isidore Geoffroy estimates that it must have 

 contained 10 qua'rts of substance, or nearly six 

 times as much as an ostrich's egg, 148 times as 

 much as an ordinary hen's egg, and 50,000 times as 

 much as that of a humming bird. Notwithstand- 

 ing, however, that in the class of birds there is a 

 general correspondence between the size of the egg 

 and the stature of the adult, this correspondence is 

 not regular or constant, and Prof. Owen has illus- 

 trated this fact in a striking manner by reference to 

 the Apteryx of XP.W Zealand, which produces a 

 proportionally very large egg. 



indication of the relative amount of repro- 

 ductive power in the three groups before dis- 

 tinguished. Thus, in the human species, the 

 two ovaries weigh about 500 grains ; in the 

 fowl, when developed at the breeding season, 

 the ovary, with its yolks, may weigh 1,500 

 grains ; and in the lump fish, above mentioned, 

 the ovaries weighed together 3 Ibs. and 3 

 ounces, or 22,300 grains. Thus the ovaries 

 were to the body, in the first, as 1 to 1,800 ; 

 in the second, as 1 to 13 ; and in the third, as" 

 1 to 3.* 



The following table may serve to exhibit 

 these proportions in a general way : 



Weight in Grains of the 



Ovum. Ovaries. Foetus. Adult. 

 Mammifer - 0001 500 45,000-0 900,000. 

 Fowl - - 900-000 1500 600*0 20,000. 

 Osseous fish - 0-135 22,300 O'l 66,500. 



Number of ova. The number or quantity 

 of the ova which the females of different 

 animals are capable of producing in a given 

 time, or during the whole of their lives, is so 

 various, that only a very vague statement can 

 be made in regard to it. The very great pro- 

 ductiveness or fecundity of osseous fishes, 

 and of many of the invertebrata, is well known. 

 The ovary of the herring has been found to 

 contain 25,000 ova. In the Cyclopterus 

 lumpus, before referred to, the number of 

 ova estimated as being contained in the ripe 

 ovaries together was about 155,000; and 

 in the ovaries of a Holibut or Hippoglossus, 

 of 156 Ibs. weight, I found about three and 

 a half millions. The queen ant of the African 

 termites is said to lay 80,000 eggs in 24 

 hours ; and the common hair worm, or Gor- 

 dius, as many as 8,000,000 in less than a 

 day. The Entozoa appear to produce the 

 greatest number of all animals a fact which 

 is somewhat surprising, when we consider how 

 few of these animals comparatively reach their 

 adult condition. In many of the above 

 animals this enormous production is not a 

 single act, but is repeated again and again in 

 successive seasons. 



In birds and those animals belonging to the 

 second group, in which the eggs are propor- 

 tionally of large size, comparatively few of the 

 ova, of which the germs are visible in the 

 ovaries, come to maturity ; and in the natural 

 state only a small number are productive. 

 But it is well known that great variations may 

 be caused in this respect by the condition of 

 the animal ; and that in a state of domesticity, 

 and under high feeding, a much greater num- 

 ber of eggs may, in some birds, come to ma- 

 turity, as in the common fo\vl t in some kinds 

 of which, indeed, an egg is laid daily for two- 

 thirds of the year a production which 

 would amount to upwards of 30 Ibs. or ten 

 times the weight of the whole animal ; and, if 



* The Article "Zeugung" by Leuckart, con- 

 tained in two parts of K. Wagner's Handworterbuch 

 der Physiologic, and which I have only received 

 since the above was written, may be consulted as 

 containing fuller information on the same and the 

 following subject. 



