The lens . 1872.] The DiatomacecB of Lake Michigan. 41 towards the extremities, the outer row on each side next the am- bulacral areas being composed of plates from two to four times as large as the plates in the remaining rows. Ambulacral areas with four rows of plates, pierced with eight rows of pores, arranged in two sets, each occupying a width of about a tenth of an inch. The exterior pores, in each pair, are so crowded towards the extremity of their respective plates, ^ ^ ^, . •^ . Oligoporus Groveri. Showing that they fall nearly, or quite, in the position of pores on ambuiacrai same li
The lens . 1872.] The DiatomacecB of Lake Michigan. 41 towards the extremities, the outer row on each side next the am- bulacral areas being composed of plates from two to four times as large as the plates in the remaining rows. Ambulacral areas with four rows of plates, pierced with eight rows of pores, arranged in two sets, each occupying a width of about a tenth of an inch. The exterior pores, in each pair, are so crowded towards the extremity of their respective plates, ^ ^ ^, . •^ . Oligoporus Groveri. Showing that they fall nearly, or quite, in the position of pores on ambuiacrai same line, while the inner ones present two more scattered lines of dots on each side of this central line. As nearly as can be judged from the fragment, the entire animalcould not have been less than five inches in diameter. O. S, Westcott Chicago High School, yuly, THE DIATOMACEJB. OF LAKE ML CHI G AN. The city of Chicago derives its water-supply from Lake Michi-gan, which washes its eastern front. Commencing on the lakeshore at a point about three-quarters of a mile north of the mouth ofthe Chicago river, which is a nearly stagnant stream, reeking withthe filth of the city poured into it by numerous sewers, a tunnel,two miles in length and six feet in diameter, has been constructedunderneath the bed of the lake. At the eastern extremity of thetunnel is located a structure, built of wood and stone, known as theCrib, surrounding and covering its mouth. At the shore end of thetunnel are the pumping-works. The water-supply enters the crib through gates in its sides, aboutten feet above the bed of the lake, and thirty feet below its surface,the water at this point averaging not far from forty feet in passes directly into and through the tunnel to the pumping-works,by which it is forced, under the pressure of a perpendicular columnof water n
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Keywords: ., bookcentury1800, bookdecade1870, booksubje, booksubjectmicroscopy
