252 Transactions. — Zoology. 



the embryo exhibits characters of special interest. It is now 

 far advanced m development, though there is still a very large 

 quantity of unused yolk in the yolk-sac. The limbs are well 

 formed, the tail is long, and the head large and very similar 

 to that of a tortoise, a resemblance which is to a large extent 

 retained even in the adult. On the snout is the sharp-pointed 

 shell-cutter ; and the body is marked with longitudinal and 

 transverse bands or stripes of alternate grey and white, a pat- 

 tern which is completely lost in the adult animal, which is 

 characteristically spotted. Thus the Tuatara conforms to what 

 appears to be a general law of coloration amongst the higher 

 vertebrates, for it has been observed in many different types — 

 e.g., the emu —that the young animal is striped even when the 

 adult is not striped ; and there is good ground for believing 

 that striping was the first kind of pattern to make its appear- 

 ance in the ancestors of existing vertebrates. 



Perhaps the most remarkable feature of stage R, however, 

 is the plugging-up of the nostrils by a dense growth of cellular 

 tissLie, and it is a truly remarkable fact that the only other 

 animal in which this embryonic character has been observed 

 is the Kiwi (Aj^terijx), in which it was described some years 

 since by the late Professor Parker. Why should two animals 

 so widely separated zoologically as the Tuatara and the Kiwi, 

 and both confined to New Zealand, exhibit this extraordinary 

 feature of development ? Has the plugging-up of the nostrils 

 in the Tuatara anj' relation to the hibernation of the embryo, 

 and, if so, why does the Kiwi exhibit the same character ? 

 These questions I fear it is impossible to answer in the pre- 

 sent state of our knowledge. 



At stage S the embryo has acquired nearly all the characters 

 of the adult : the yolk is all absorbed, and the young animal 

 hatches. One fact only needs to be mentioned here about this 

 stage, and that concerns the teeth. In the adult Tuatara, a3 

 is well known, there are two very large cutting-teeth in front 

 of each jaw, upper and lower. At stage S each of these four 

 teeth is represented b}- three separate conical cusps, which 

 evidently grow together with advancing age to form the very 

 characteristic front teeth of the adult. 



As regards the details of the development of the special 

 organs much still remains to be done, and in this work I have 

 been very fortunate in securing the co-operation of eminent 

 speciahsts in England. Professor G. B. Howes, LL.D., F.E.S., 

 has most kindly consented to undertake the investigation of 

 the development of the skeleton, and has already commenced 

 the work, with the assistance of one of his students. Happily 

 I received a further supply of eggs from Mr. Henaiihan in De- 

 cember last, which have afforded much valuable material for 

 further investigation. Two other English specialists have also 



