a 
THE AUSTRALIAN NATURALIST. 141. 
skull, and in some lizards is covered only by a transparent scale. 
For many years the meaning of this structure lay in obscurity, 
and some remarkable functions have in the past been attributed 
to it by the older physiologists, but recent researches have 
shown it to be really a degenerate eye. It retains its highest 
state of development in the lizards and some of their allies, and 
is still insome slight degree functional in many of them. Itis 
very well seen in a section, shown here to-night, of the head of 
Lygosoma quoyt, « skink common in the neighbourhood of 
Sydney. 
Many lizards have lost their limbs and assumed a very snake- 
like form. We find that the habit of living in burrows in the 
ground is accompanied by a partial or complete reduction in the 
limbs. ‘This loss of the limbs, too, is often correlated with an 
elongation of the trunk and tail, so that the snake-like form is 
emphasised. 
Reduction of the limbs has occurred in a number of families 
not directly related to one another, so that the absence of limbs 
must not be taken as indicating a relationship, but merely asa 
striking example of retrogressive convergent evolution. That 
is to say this similar feature, the loss of limbs, isa degenerative 
change that has appeared in a number of different families of 
lizards, through the operation of similar causes. This loss of 
limbs often does not occur in all the members of one family. 
Jiven in the same genus some of the species may have the 
limbs well developed, while others have them much reduced. 
It has already been mentioned that there is one genus of 
lizards, the members of which are poisonous. This genus, 
Heloderma, contains only two species, which live in Mexico and 
Central America. These are the only known poisonous lizards 
in the world, so that there are no poisonous lizayds in Australia. 
In spite of this quite a number of our lizards have a very bad 
reputation, and are supposed by many people to be very 
dangerous. The little wood-adder, Gymnodactylus platurus, is 
one of the geckos with a flattened somewhat leaf-like tail, and 
this and another gecko, Wdura robusta, living on old logs, are 
supposed to be very poisonous, But not only have they no 
poison, but they are very inoffensive and gentle creatures, 
and cannot bite hard enough to hurt a child. The same 
remarks apply to one of our legless lizards, Lialis burtont, one 
of the most harmless creatures In the world. Several times in 
different parts of the country [have been told about a very 
dangerous snake found living in the district, and when a speci- 
men has been forthcoming, generally in a much-battered con- 
dition, it has turned out to be this poor little Lialis. Itis very 
hard to understand how such undeserved reputations have been 
made. 
