THE DEVELOPMENT OF CITIES. 391 



stickleback, and the fishing-frog, or angler, and the salmons and the 

 cod, and the herring, afford inviting objects of curious observation, or 

 scientific and economical study or speculation, concerning the later 

 results of which we have kept the readers of " The Popular Science 

 Monthly" informed. The last fish we notice is the eel, the manner of 

 the reproduction of which is yet a puzzle to naturalists. Dr. Gimther 

 says of it: 



" Their mode of propagation is still unknown. So much only is 

 certain, that they do not spawn in fresh water, that many full-grown 

 individuals, but not all, descend rivers during the winter months, and 

 that some of them, at least, must spawn in brackish water or in deep 

 water in the sea ; for in the course of the summer young individ- 

 uals, from three to five inches long, ascend rivers in incredible num- 

 bers, overcoming all obstacles, ascending vertical walls or flood-gates, 

 entering every larger or smaller tributary, and making their way even 

 over terra firma to waters shut off from all communication with rivers. 

 Such immigrations have long been known by the name of ' eel-fairs.' The 

 majority of the eels which migrate to the sea appear to return to fresh 

 water, but not in a body, but irregularly, and throughout the warmer 

 part of the year. No naturalist has ever observed these fishes in the 

 act of spawning, or found mature ova ; and the organs of reproduc- 

 tion of individuals caught in fresh water are so little developed, and 

 so much alike, that the female organ can be distinguished from the 

 male only with the aid of a microscope." 



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THE DEVELOPMENT OF CITIES. 



By M. BADOEEEAU. 



THE rectangular system of laying out streets has the advantage of 

 extreme simplicity, and lends itself to a convenient adjustment 

 of the interior of the houses of a city ; but it is monotonous in the 

 extreme, and makes communication between one quarter of the town 

 and another very inconvenient ; for the passenger is compelled to go 

 along the two sides of a triangle to accomplish the distance repre- 

 sented by its hypotenuse. We have endeavored to solve the problem 

 of the best way of arranging the streets of cities by mathematical cal- 

 culations, but have found the task one leading to geometrical compli- 

 cations. We recommend the study to geometricians as an interesting 

 one, and content ourselves here with stating the conclusions we have 

 reached. We have examined the question in the two forms : By what 

 law can we arrange the streets so as to lose the least possible amount 

 of space, and still have the greatest possible length of roads ; and, 

 given a surface of which the shape and area are known, and the law of 



