PROGRESS OF MICROSCOPICAL SCIENCE. 283 



of organization ; the results can be extended to the whole animal 

 kingdom, and receive a general signification. 



" However, of all the types of organization, that which serves best 

 for research on this capital question of the origin of organic systems, 

 is that of the polypes, still called zoophytes or Coelenterates. In 

 them, in short, the ectoderm and endoderm persist with their embry- 

 onic characters during their entire life ; all the organs of the zoophytes 

 are only a dependence of one or the other of these layers, sometimes 

 of the two layers united. 



" The polype form may be traced back with the greatest facility 

 to the Gastrula, all the jjarts of which are preserved without under- 

 going any great modifications during all the course of existence. 



" Conclusions. — In the Hydractiniee, 1. The eggs are developed 

 exclusively from the epithelial cellules of the endoderm. They remain, 

 up to the time of their maturity, surrounded by the elements of the 

 endoderm. 



" 2. The testicles and spermatozoa are developed from the ecto- 

 derm; this organ results from the progressive transformation of a 

 primitive cellular fold formed by invagination. 



" 3. There exists in the female sporosacs a rudiment of the tes- 

 ticular organ ; in the male sporosacs a rudiment of an ovary. The 

 sporosacs are then morphologically herma2)hrodites Fecunda- 

 tion consists in the union of an egg, a product of the endoderm, with 

 a certain number of sj^ermatozoa, products of the ectoderm. This act 

 has no other end than to unite chemical elements of opposite polarity, 

 which after having been united an instant in the egg, separate again ; 

 for in most animals those in which the division of the vitellus into two 

 occurs, the elements from which the ectoderm are formed are already 

 separated from those which are to form the internal layer of the 

 embryo. 



" The new individuality is realized at the instant when the union 

 between the elements of opposed polarity has taken place, as abso- 

 lutely as a molecule of water is formed by the union of atoms of 

 hydrogen and oxygen." 



The Origin of Typlio'ul Fever. — In the beginning of the month of 

 November a very imj)ortant letter of some length on this subject 

 appeared, from the pen of Dr. Tyndall, F.E.S., in ' The Times ' news- 

 paper. We would commend the letter to the attention of those of our 

 readers who are interested in the subject. We difier from one of our 

 contemporaries in the view we take of this letter ; for, unquestionably, 

 although its facts are not novel to the scientifically educated medical 

 man, still, to the mass of surgeons, and to the whole of the non- 

 medical community, it is absolutely and completely novel. And it 

 seems to us that a certain amount of ci-edit is due to Professor Tyndall 

 for thus manfully coming forward to discuss, in a purely popular form, 

 facts which he, of course, knew were well enough known to certain 

 professional minds. He has at once spread throughout the country 

 views which, had he not come forward, might have remained where 

 they had been till the next half century. 



