340 ANNUAL OF SCIENTIFIC DISCOVERY. 



overlooked. So far as known, it has always been the custom every- 

 where to sell eggs by number, without respect to size, weight, or pe- 

 culiar quality. Yet no absurdity can be greater. It has been ascer- 

 tained, by careful experiments recently made by the author, that the 

 fair average weight for a dozen of eggs is 22k oz. Recently, on appli- 

 cation to a provision-dealer, he made answer to the inquiry addressed 

 to him, that he made no difference in the price of his eggs. On exami- 

 nation of his stock, it appeared that the largest eggs weighed 24 oz, 

 per dozen, and the small*^t only 14o oz. In the one case, a fraction 

 over eleven eggs would equal the average weight of a dozen, and in 

 the other it would require over 18 eggs to reach the proper weight. 

 It appeared, to our mutual astonishment, that the difference in weight 

 between the two kinds was about one half, while the price was the 

 same. Dr. Bennett's Poultry Book. 



/ 



PARASITES AND THEIR RELATIONS TO OTHER ANIMALS. 



AT a meeting of the Boston Society of Natural History in February, 

 Dr. Burnett presented a communication on the relations of an order of 

 parasites (lice) to the different Fauna, as bearing, first, on the distinct 

 creation of types of animals, and, second, on the local creation of these 

 types wherever they are found. In the general Fauna of the earth, the 

 fact that totally distinct genera and species exist, exposed to the same 

 external influences, is a strong argument against their being the results 

 of modifications of a single type, and in favor of their having been 

 created as we now see them. The same is true as regards these par- 

 asites ; we have different species, and even different genera, upon a 

 single animal, all exposed to the same external changes. If genera 

 and species are mere modifications of a primitive family type, \TC 

 should expect to find a uniformity in the special character of parasites 

 in all the species of the genera of that family. For instance, if the 

 Sciuridae are but modifications of a primitive type Squirrel, we should 

 expect to find certain parasites common to all, with a uniform specific 

 character, without widely separated genera ; which, as far as his ex- 

 perience goes, is not true, for though in many cases certain species of 

 parasites are common to the whole family, yet there is an evident ten- 

 dency for each species of the higher animals to have its own peculiar 

 species of parasites. Though we can easily imagine that the same 

 species may be found in mammals and birds of the same family, with 

 similar habits, and associating together, \ve cannot understand that 

 the same species of parasite should be found in widely different fami- 

 lies, of entirely dissimilar habits ; yet such is the fact, and it is not 

 reconcilable with the hypothesis of a successive production of types 

 by a series of changes of their structure ; on the contrary, it would go 

 to show that the existing specific types were as such created. 



As to the local creation of genera and species, we know that the 

 existence of the world's animals has not that commonness which might 

 be supposed ; they have relations of a local nature, connected with a 

 remarkable diversity of forms. At any rate, this fact is certain, that 

 each particular region has a marked tendency to have its own peculiar 



