The Visual Cells in Vertebrates; Chiefly in Necturus Maculosus (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated.1908 Excerpt: ... rendered me every encouragement by helpful suggestions and valuable criticism. I am indebted to Dr. E L. Mark for the excellent opportunities of the Harvard Zoological laboratories and for help in the arrangement of plates, as well as kindly interest at all times. Thanks are due Professors J. E. Wolff and Charles Palache for apparatus and assistance in the use of the same; also to Doctors F. B. Mallory and F. H. Verhoeff for suggestions in technique. In addition to these, there are many to whom I am under obligation for kindly assistance. To these I wish here to express my thanks. II. OBSERVATIONS. A. General Methods And Techn1que. I began my study of the visual cells in the frog, Rana pipiens Shreber, because of the ease with which this animal can be obtained at all seasons, and because of the large size of its elements. The importance of the latter consideration is obvious and led me finally to study the retinae of the large salamander, Necturus maculosus Rafinesque (1819), the "Mud-puppy" of the St. Lawrence and Mississippi basins. The rods in this species proved to have a diameter two and a half times that of the rods in the frog, and larger than those of any other vertebrate known to me. This is in keeping with the well known fact that in Necturus, the histological elements are unusually large, the red blood corpuscle being the largest red corpuscle known. As this animal is commonly kept by dealers for supply to zoological laboratories, it can be obtained readily before ice appears and kept alive in laboratory tanks with running or standing water, of a depth just sufficient to cover it. The size of the visual elements in Necturus led me to use them in preference to those of the frog as a basis for my studies. The advantage of size outweighed the two di...