52 MAMMALIAN DESCENT. [Lect. IL 



but the l)ones and cartilages that encapsule it were; carefully (l('scril)ed, 

 and copiously illustrated. In those types we have the cidmination 

 of these organs, which have some mysterious connection witli the 

 organ of smell ; the Jirst or olf actor ij nerves give oft" fibres to them. 

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

 decline in Man, who, however, in an early stage, possesses them, as 

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

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

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

 excellent " Summary " in the Jcmrnal 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 Avliat it was in ancestral 

 forms." 



Is^ow, 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 INIan, these organs are 

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

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

 deplorably agnostic condition with regard to these organs, they may 

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

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

 Ornithorhynclms (the size of a moderate list, with the hair appear- 

 ing), these parts and their ca})sules are as large as in Serpents 

 and Lizards. In the INIarsupials, Edentates, and Inseotivores 

 they are Avell developed in the embryo up to the time of liirth, 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 emljryo ; and the liones and 

 cartilages that support them are more persistent than the organs 

 themselves. In the Eeptiles, these organs are mostly invested l)y bone, 

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

 wards from the snout. In the j\Iannnals oidy one pair of small bones 

 assists in protecting the soft gland-like organ ; in the Re})tiles it lies on 

 each 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 



