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it passes. Thirdly, the plankton is unequally distributed in the various vertical zones or strata of the water; for instance, certain groups are characteristic of the surface stratum, others of the bottom stratum, and still others of the various intermediate strata. The determination of the various groups characteristic of these different strata constitutes one of the most important features of the collector's efforts. It is evident that with the net we cannot collect the plankton of one stratum without mixing it with others. Fourth, ice precludes the use of the net during the winter months, which, in fact, represent the best season for plankton work.
These, together with other difficulties, have led students to seek other means of collecting. Among other forms of apparatus in recent use is the plankton pump, a machine very similar to the force pump. While the pumping method cannot be said to eliminate all the disadvantages mentioned, yet we may say that it reduces these difficulties to a minimum. The writer determined last fall to attempt the construction of a light plankton pump that might be carried about and operated by one person; a simple plan of construction was suggested by Dr. H. B. Ward. This plan, with some modifications, finds embodiment in the pump as it now stands.*
The instrument is practically a force-pump, whose form and mode of operation are indicated in the accompanying plates. The cylinder of the pump is 11x3] inches and has a capacity of 3477 cubic inches per stroke. The stroke of the piston is definite in length and is regulated by a lock-nut as shown in the plate. The valves used are finely ground check-valves, to which, it is believed, the accuracy of the working of the apparatus is largely due. The pump is connected with the water by a hose 11 inches in diameter, whose lower end is adjusted to the various vertical zones of water by means of attachment to a floating block.
The net was constructed primarily for collecting crustacea. It consists of a tin cylinder (g, Fig. 9) 6x6 inches, to 'which is
*The writer is greatly indebted to Prof. C. D. Rose for valuable hints in the construction of the apparatus.
soldered a truncated cone; to the lower end of the conical part is attached the filtering apparatus (h), which is a cylinder 4x1.) inches, made of fine wire gauze containing eighty-three meshes to the linear inch. The upper portion of the tin cylinder has fitted to it a detachable rim, by means of which a net cover may be attached to the apparatus for the purpose of preventing
FIGURE 8.—Sectional view of the pump, showing direction of the
current as the piston rises.
the entrance of objectionable matter. To the rim mentioned are attached the supports (f) as shown in the figure. The filtering apparatus is so constructed that a net of bolting cloth may be attached outside of the gauze filter, thus adapting the instrument (which may be used separately) for the various work
of the ordinary net. Most gratifying results have attended the use of this pumping apparatus during the last few weeks. It is possible with it to measure with almost absolute accuracy the amount of water filtered. The average amount water thrown at each stroke is 3474 cubic inches. Careful tests show that the greatest variation above this average is 1.9%, and below only 1.3%, thus making the extremes between the least and the greatest amount thrown but 3.2%. The collecting can be carried on without any disturbance to the water, and the water can be drawn from any stratum, thus enabling one to get the vertical distribution of the plankton.
Material has been collected from the midst of debris and also during the winter months when the water was covered by a thick coat of ice.
EXPLANATION OF FIGURE 9. c, Cylinder of pump ; e, handle of piston rod; d, lock-nut ; b, check valves; k, attachment of hose ; i, distal end of hose ; g, cylinder of net; h, filtering apparatus; f, support.
THE PARASITES OF NEBRASKA DOGS AND CATS.
HENRY BALDWIN WARD.
From a biological standpoint parasites constitute a group of great importance. The forms included under the term are members of widely separated families which have acquired similar habits and by virtue of like conditions in their environment have manifested convergent variation, departing at times so widely from the primitive type that their relationship was long misunderstood and in numerous instances is even yet a matter of doubt.
These forms are, however, of no less economic importance since they are responsible for some of the serious ailments which fall upon man and his closest allies, the domesticated animals. From both standpoints, then, the group of parasites deserves the closest study, and yet, despite its importance, but little has been accurately determined concerning the distribution and frequence of these forms in our own country.
The intimate relations in which the domestic animals stand to man have always made the transfer of parasites from one to the other a matter of much greater probability than exists between man and other forms of animal life. It is but natural that the most common species of human tapeworm come to man from his two chief sources of animal food, beef and pork. The chances of accidental infection, however, are evidently much greater in the case of those forms that are intimately associated with man, and hence clearly greatest in those which he holds as household pets, -the dog and the cat. It is also evident that the chances of parasitic infection are greatest in the case of those peoples or individuals who live on terms of closest intimacy with these domesticated forms. Thus, the Icelander, who is known to permit his dog to occupy, not only the same room, but even the same
bed with himself, is most seriously troubled with the parasites common to dogs and man, and the infant or child is more likely to be infected than persons of maturer years.
It becomes, then, a matter of great importance to determine in any region or community what is the average percentage of these animals infected with parasites, since, as will be evident later, the percentage of infection varies widely in different regions. It is, however, by no means a matter of indifference what parasites occur in the dogs or cats of a specific locality, for certain of the species are entirely foreign to the human race, not being known to be at home in man at any stage of his existence, and certain species are comparatively harmless, even when present, while certain others are the causes of grave disorders, among them the most serious parasitic disease which is known. In a paper on the prevalence of Entozoa in the dog, and their relation to public health, published in 1867 by Dr. Cobbold, of London, perhaps the most eminent helminthologist that England has ever produced, the author emphasizes again and again the importance of helminthological studies on this animal, and the necessity of extended knowledge concerning the number and kinds of its parasites. It seems, then, of importance to ascertain for Lincoln the extent to which its canine population is infected as well as the species of parasites which occur in dogs here. The cat, although not so closely associated with man and not furnishing him with so many species of parasites, has also been included within the limits of this investigation, During the last three years a large number of animals of both species have been carefully examined for parasites and the results of the examination recorded. For kindly assistance in this work I am indebted to a considerable number of students, who have been connected with the University during this time. The final examination and determination of the parasites, as well as the tabulation and discussion of the same', are the results of my own study. Many other animals of these species have been examined in part, or, owing to circumstances, with less care; they have not been considered in the tabular results given, although no facts have been observed which do not bear out the conclu