io M. Coste' s Memoir. 193 



science.* M. Coste however is desirous that his readers should 

 believe that the impediments which he overcame in the dis- 

 covery of the allantois in my second ovum, were too great for 

 me in the dissection of my first ovum ; and that the allantois 

 was present in that ovum, but overlooked by me. However, 

 the membranes of my marsupial ovum of 1834, are simply 

 stretched out in the preparation; nothing is removed save the 

 small portions of the external membrane, which I then sub- 

 mitted to microscopical observations. This ovum M. Coste 

 examined whilst he was in England; and I can only say that 

 if he had found the allantois there, he would have made a 

 real discovery. 



M. Coste, however, again appeals to analogy in proof of his 

 suspicions, that an allantois must have been present in this 

 ovum, but he is not more fortunate in this, than in his pre- 

 ceding attempt in that line of argument. He says, "M. Owen 

 n'ignore pas que 1' apparition de l'allantoide est anterieure a 

 certaines phenomenes qui, chez les carnassiers, les ruminants, 

 les rongeurs, et les oiseaux meme, correspond a une epoque 

 primordiale du developpement. 11 sait, par exemple, qu'elle 

 precede de beaucoup la formation du cordon ombilical." I 

 have here certainly to admit my ignorance of the correspon- 

 dence between the carnassiers &c. and the birds, in the pe- 

 riod of the developement of the allantois. So far from the 

 allantois being developed at the primordial epoch of embryo- 

 logical developement in the bird, my researches in that class 

 have shewn me that it does not take place until the embryo 

 has made a certain progress in developement ; until the head 

 is well distinguished from the trunk, the eyes plainly percep- 

 tible, and the rudiments of the four extremities have begun to 

 bud forth. In the Rodentia and Ruminantia, and in all the 

 placental Mammalia, of which the developement has hi- 

 therto been traced, the allantois, which is the prime agent 



*In my notes to ' Hunter's Animal Economy,' to which I first consigned 

 my discovery of the allantois in question, I drew the following inference 

 from the imperfect state of its developement. " When the extremities are 

 formed, and the uterine foetus has attained about two-thirds of its size, an 

 allantois is developed ; the umbilical arteries co-extended with this sac, do 

 not, however, as in the placental Mammalia, pass to the chorion, and con- 

 sequently there is no adhesion of the foetal membranes to the uterine pari- 

 etes, and therefore, no obstruction to the escape of the embryo from the ute- 

 rus into the vagina." 



I here consider the condition of the allantois as one of the accessory 

 causes of the premature birth of the marsupial embryo : it harmonises with 

 many other modifications, all tending to the same result. With M. Coste 

 the state of the developement of the allantois is the sole cause of the avorte- 

 ment of the embryo. See p. 24. 



