PROGRESS OF MICROSCOPICAL SCIENCE. 229 



outer zone the smaller part of the cells. 2. In the first period of 

 digestion, during which a plentiful secretion occurs, there is diminution 

 of the entire cells by using up of the granular inner zone, then addition 

 of new materials to the outer zone, so that this becomes enlarged. 3. In 

 the second period of digestion, during which the secretion diminishes 

 and comes to a standstill, there is a new formation of the granular 

 inner zone at the expense of the homogeneous outer zone, most pro- 

 nounced diminution of the latter, increase of all the cells. 4. With 

 long-continued hunger there is gradual increase of the latter to their 

 original dimensions, and therewith slight diminution of the inner zone. 

 During the state of physiological activity there is a continual change 

 in the cells — metamorphosis internally, addition of matters externally. 

 Internally there is conversion of the granules into secretory constituents, 

 externally employment of the nutrient materials for the formation of 

 the homogeneous substance, which again becomes converted into granular 

 masses. The average appearance of the cells depends upon the relative 

 rapidity vAith which this process occurs. In the first period of change 

 there is a more rapid consumption internally and more rapid addition 

 externally : in the second period, the most rapid changes occur at the 

 limit between the outer and inner zones, in that the substance of the 

 former becomes converted into that of the latter. 



The Development and Succession of the Poison-fangs of Snakes. — A paper 

 was read at a late meeting of the Koyal Society which had been written 

 by Mr. Charles S. Tomes, M.A., and which is published in the follow- 

 ing abstract in the last number of ' Proceedings of the Eoyal Society.' 



At the conclusion of a paper upon the development of the teeth of 

 Ophidia, published in the first part of the ' Philosophical Transactions ' 

 for 1875, I noted that there were peculiarities, which I had not then 

 been able to understand, in the succession and development of the 

 poison-fangs. Having reviewed the literature of the subject in that 

 and in a preceding paper on the development of Amphibian teeth, I will 

 pass at once to the description of the special features which distinguish 

 the development of poison-fangs. Poisonous snakes are divided into 

 two groups — those which have a shortened movable maxillary bone, 

 which carries the poison-fang and another tooth ; and those which have 

 the maxillary bone longer, immovable, and often carrying other teeth 

 behind the poison-fang. 



In the former, or viperine poisonous snakes, the poison-fang is very 

 long, and, when out of use, lies recumbent ; in the latter, or colubrine 

 poisonous snakes, it is, from the maxillary bone being fixed, constantly 

 erect.* 



As'fresh specimens are indispensable for a complete investigation 

 of developmental peculiarities, I have only been able to examine one 

 of the colubrine group, viz. the Indian cobra. 



Of it one may say, roughly speaking, that the poison-fangs are 

 developed just like any other Ophidian teeth, for a description of 

 which I must refer to my former paper, save only that the tooth-germs 

 are necessarily individually modified so as to produce the characteristic 

 canaliculated poison-tooth. 



* Gunther's ' Reptiles of British India,' p. 165. 



