52 MAMMALIAX DESCENT. [Lect. IL 



but the bones and cartilages tbat encajDsule it were carefully described, 

 and copiously illustrated. In those types we have the culmination 

 of these organs, which have some mysterious connection with the 

 organ of smell ; the first or olfactory nerves give off fibres to them. 

 If these organs have their height in these Eeptiles, they have their 

 decline in Man, who, however, in an early stage, i^ossesses them, as 

 Professor A. KoUiker's invaluable researches show, both those .pub- 

 lished at Leipzig in 1877, and those much later, at Wtirzburg in 1883. 

 For an abstract of this last piece of research I am indebted to the 

 excellent " Summary " in the Journal of the Royal Microscopical 

 Society, for April 1884, pp. 201-203. The concluding sentences 

 of this abstract are as follows : — " From the rich possession of nerves 

 by Jacobson's organ in an eight-week old embryo, and their dis- 

 appearance in older embryos, we may conclude that the organ is now 

 in a rudimentary condition as compared with what it was in ancestral 

 forms." 



XoAv, on one hand, in Serpents, and Lizards, we have these organs 

 and their related skeletal parts, both cartilaginous and bony, highly 

 developed and persistent, and on the other, in Man, these organs are 

 soon aborted ; nor am I aware that the skeletal parts that should 

 supjjort them are more than feebly developed. Although we are in a 

 dejilorably agnostic condition with regard to these organs, they may 

 Ijc used as a measure of the height of any mammal or order of 

 mammals, in the scale of life. In my young specimens of 

 Ornithorhynchvs (the size of a moderate fist, with the hair appear- 

 ing), these parts and their capsules are as large as in Serpents 

 and Lizards. In the Marsupials, Edentates, and Insectivores 

 tliey are well developed in the embryo up to the time of birth, and 

 for some time after, having considerable persistence in several at 

 least of those kinds. They are present in all sorts of mammals, as 

 far as research has gone, at least in the embryo ; and the bones and 

 cartilages that support them are more persistent than the organs 

 themselves. In the ReptUes, these organs are mostly invested by bone, 

 in the Mammals they are well encapsuled by cartilages growing back- 

 wards from the snout. In the Mammals only one pair of small bones 

 assists in protecting the soft gland-like organ ; in the Eeptiles it lies on 

 oacli side, as in a dish, formed by a bone, the so-called vomer (plough- 

 share), and it is covered in by another bone which serves as an elegant 



