OUTLINES OF ECONOMIC ZOOLOGY REESE OUTLINES OF ECONOMIC ZOOLOGY BY ALBERT M. REESE, Ph. D. PROFESSOR OF ZOOLOGY IN WEST VIRGINIA UNIVERSITY W11H 194 ILLUSTRATIONS PHILADELPHIA BLAKISTON'S SON & CO 1012 WALNUT STREET COPYRIGHT, 1919, BY P. BLAKISTON'S SON & Co. THK M A. P 1, E PKKSS YOKK PA. PREFACE While there are a few so-called "economic zoologies" on the market, there is none known to the author that makes the economic aspect of the subject the main, point of attack, with morphology, habits, etc., secondary. Hence this volume which is based upon a brief course in economic zoology given by the author for several years in West Virginia University. The book may be used in several ways. As followed by the author, the course may be given as a separate one to students who have already had the regular elementary course in general zoology. In this case the students will be familiar with the classification, structure and habits of most of the type forms discussed, but, if desired, additional labo- ratory work maybe arranged for the study of certain parasitic and other economically important forms not generally considered in a general laboratory course. Or, the text might be used in a beginning course in zoology by some amplification of the morphologic and other aspects and considerable increase in laboratory work. Again, it could well be used as supplementary reading with, say, one hour credit per semester for the year, in connection with the regular elementary course in general zoology. It is thought that, used in one or other of these ways or in some still different way, it should be especially useful to students in agriculture, who want a "practical" course. Various sources of information have been drawn upon, and recognized authorities in each subject consulted so far as possible. The publications of the Government, especially those of the Department of Agriculture, have been freely used and quoted. The figures have been borrowed largely, either from technical or from more popular works, whichever gave the best ideas of the animals portrayed; the source is indicated in every case. The brief bibliography at the end of the book is merely to aid the student, who may have become especially interested in some animal or group, to get more detailed information. 393366 VI PREFACE The author is much indebted to Mr. E. W. Nelson, Chief of the Biological Survey of the United States Department of Agriculture, and to some of his specialists, for reading the proofs of this book and for various changes suggested. ALBERT M. REESE. WEST VIRGINIA UNIVERSITY, MORGANTOWN, W. V"A. CONCERNING THE IMPORTANCE OF ECONOMIC ZOOLOGY "In its relation to public welfare economic zoology is of the most vital and far-reaching importance. Animal life, from its lowliest organisms, among which lurk some of our deadliest foes as well as beneficent friends, to the highest verte- brates, touches and effects our lives and welfare in innumerable ways. It must be studied in all its phases as never before to guard against previously unsuspected or little known diseases of man and domestic animals, as well as to develop the wealth and ever-increasing variety of products from which we obtain food, medicines, clothing, dyes, ornaments, and an endless number of other useful articles. No man can now be considered well informed who has not a considerable knowledge of economic zoology in its more direct relationships to human life, while to the scientific investigator the subject has the charm of endless variety and service to mankind." From an address delivered at Baltimore on December 28, 1918, by Mr. E. W. Nelson, Chief of the United States Biological Survey. "On the whole, I think that there is no branch or stem of zoology now so im- portant to this world as economic zoology; and in the teaching of it the vast majority of America's higher institutions of learning are fully twenty-five years behind the times. "I have made at least six attempts to induce universities and colleges to establish chairs of economic zoology, and have failed in all save one." From a personal letter from Dr. Wm. T. Hornaday, Director of the New York Zoological Park, written December 30, 1918. vn CONTENTS CHAPTER I PAGE PHYLUM PROTOZOA i Class Rhizopoda i Class Mastigophora 3 Class Sporozoa 4 Class Infusoria 10 CHAPTER II PHYLUM PORIFERA n CHAPTER III PHYLUM CCELENTERATA 15 Class Hydrozoa 16 Class Scyphozoa 16 Class Anthozoa 17 CHAPTER IV PHYLUM ECHINODERMATA 20 Class Asteroidea 24 Class Echinoidea 24 Class Holothuroidea ; 24 Class Ophiuroidea 25 Class Crinoidea 25 CHAPTER V PHYLUM PLATYHELMINTHES : FLAT-WORMS 26 Class Turbellaria 27 Class Cestoda 27 Class Trematoda 29 CHAPTER VI PHYLUM NEMATHELMINTHES : ROUND-WORMS 31 ix 10 CONTENTS CHAPTER VII PAGE PHYLUM ANNULATA , 40 Class Chaetopoda 40 Class Hirudinea 42 CHAPTER VIII PHYLUM MOLLUSCA 44 Class Lamellibranchiata 45 Class Gastropoda 58 Class Cephalopoda 66 Class Amphineura 67 Class Scaphopoda 67 1 CHAPTER IX PHYLUM ARTHROPODA 68 Class Crustacea 71 Class Onychophora 78 Class Myriapoda 78 Class Arachnida 79 Class Insecta 83 CHAPTER X PHYLUM CHORDATA: SUBPHYLUM VERTEBRATA 107 Class Pisces 107 CHAPTER XI PHYLUM CHORDATA: SUBPHYLUM VERTEBRATA. Class Amphibia 123 Order Apoda 126 Order Caudata 126 Order Anura. . 126 CHAPTER XII PHYLUM CHORDATA: SUBPHYLUM VERTEBRATA. Class Reptilia . . . 135 Order Chelonia 136 Order Lacertilia 148 Order Ophidia . 153 Order Crocodilia 170 CONTENTS XI CHAPTER XIII PAGE PHYLUM CHORDATA: SUBPHYLUM VERTEBRATA. Class Aves '....' '. 17? CHAPTER XIV PHYLUM CHORDATA: SUBPHYLUM VERTEBRATA. Class Mammalia 205 Order Monotremata 206 Order Marsupialia 206 Order Insectivora 208 Order Chioptera 210 Order Carnivora 211 Order Rodentia 227 Order Edentata 260 Order Primates 262 Order Ungulata 263 Order Sirenia 274 Order Cetacea 2 74 REFERENCES 286 INDEX. . 293 LIST OF ILLUSTRATIONS FIGURE PAGE 1. Ameba i 2. Trypanosome 3 3. Victim of sleeping sickness 4 4. Diagram to illustrate the life-history of the malarial parasite 5 5. Negri bodies 8 6. Tests of foraminifera 10 7. Colony of simple sponges 1 1 8. Colony of Obelia 15 9. Three Scyphozoa 16 10. Sea anemone .' 17 11. Ctenophora 18 12. An atoll 19 13. Starfish 21 14. Sea urchin 22 15. Sea urchin with spines removed 23 16. Sea cucumber 23 17. Serpent star 24 18. Crinoid 25 19. Planaria 26 20. Human tapeworm 28 21. Liver fluke 29 22. Parts of Ascaris lumbricoides 31 23. Cross section of Ascaris lumbricoides 32 24. Dissection of Ascaris lumbricoides 33 25. Hookworm 34 26. Trichinella spiralis 37 27. Leech 41 28. Diagram of leech 42 29. Dissection of oyster 46 30. Bed of marketable oysters 48 31. Oyster shell and pipe, with attached oysters 49 32. Tangle for collecting starfish, etc 50 33. Oyster tongs in use 51 34. Oyster dredge in use 52 35. Long-neck clam 53 36. Clam beach and rake 54 37. Long-neck clams from one square foot of flat 55 38. Hard-shell clam 56 xiii XIV LIST OF ILLUSTRATIONS FIGURE PAGE 39. Scallop 56 40. Salt-water mussel 57 41 . Abalone 58 42. Window shell 59 43. Murex ; ,v '..". . 60 44. Drilled shell of pearl mussel 63 45. Ship-worm 64 46. Octopus 64 460. Squid 65 47. Chiton 66 48. Dentalium 66 49. Cyclops 68 50. Goose barnacle 69 51. Acorn barnacle 70 52. Peripatus 70 53. Crayfish , 75 54. Rock crab 77 55. Shrimp 78 56. Centipede 78 57. House centipede 79 58. Millipede 79 59. "Tarantula" spider 80 6c. Black widow spider 81 6r. Scorpion 82 62. Acarina 82 63. King crab 84 64. Yellow-fever mosquito. 85 65. Culex and Anopheles mosquitoes 86 66. Larvae of Anopheles 87 67. Eggs and larvae of Culex 88 68. Larva and pupa of Culex 89 69. House-fly 90 70. Wing of stable-fly 91 71. Wing of house-fly 91 72. Part of leg of house-fly 92 73. Eggs of house-fly 93 74. Maggot trap for house-flies 95 75. Termites 96 76. Work of termites in walnut wood 97 77. Work of termites in book 98 78. Clothes moth 101 79. Ichneumon fly and host 105 80. Lateral view of Amphioxus 108 81. Three Cyclostomes 109 82. Dog-fish in LIST OF ILLUSTRATIONS XV FIGURE PAGE 83. Electric ray ... 112 84. Sword-fish • n8 85. Sturgeon • HQ 86. Metamorphosis of frog • 124 87. Mud-puppy, Necturus. 125 88. Hellbender, Cryptobranchus 125 89. Spotted salamander ... 126 90. Tree frog ... 127 91. Common bullfrog' • • 128 92. Leopard frog • • • ,I29 93. Spring frog -131 94. American toad *32 95. Green turtle ,- , *.. • *38 96. Carapace of diamond-back terrapin .14° 960. Pen of diamond-back terrapins 142 97. Common snapping turtle • • 145 98. Common soft-shelled turtle . 146 99. Hawk's bill turtle . U9 100. Common swift ... 151 101. Iguana - • i52 102. Dissected head of rattlesnake 154 103. Skull of a pit viper ... i55 104. Cotton-mouth moccasin . . 158 105. Copperhead • • • 160 106. Diamond rattler ... 161 107. Common water snake 163 108. Blacksnake ... 165 109. Common bull snake 168 no. Common king snake 169 in. Skins of alligator 1 73 112. Archaeopteryx , 179 1 13. Kiwi 1 80 1 14. African ostrich 181 115. Plucking an ostrich r 183 1 16. American egret 187 117. California quail 188 118. Hairy woodpecker 190 119. Great horned owl 191 120. Barn owl 192 121. Cooper's hawk 193 122. Four seed-destroying sparrows 196 1 23. Bird house 199 1 24. Bird house 199 125. Bird house 199 -126. Martin house 201 XVI LIST OF ILLUSTRATIONS FIGURE PAGE 127. Window food shelf 202 1 28. Feeding box on pole 203 1 29. Feeding box on pole 204 130. Feeding box on pole 204 131. Opossum , 207 132. Kangaroo ..,.-;.. 208 133. Common mole 209 134. Little brown bat 210 135. Karakul sheep and lamb •. .' 215 136. Black fox 216 137. Plan for fox ranch 217 138. Fox kennel and pen 218 139. Canadian otters... 219 140. Mink 220 141. Skunk 221 142. Muskrat 222 143. Beaver 223 144. Fur-seal rookery 225 145. Skull of woodchuck 227 146. Brown rat 229 147. Rat poster 232 i47a. Rat poster 233 148. Rat-proofing in barn 234 149. Rat-proofing a wooden building 236 150. Rat-proof corn crib , 237 151. All-metal guillotine rat trap 238 152. Wooden base guillotine rat and mouse traps 239 153. Wire cage rat trap 239 154. Barrel rat trap 240 155. Rat shields for ships' hawsers 242 156. Meadow and pine mice 246 157. Apple tree girdled by mice 247 158. Pile of mouse skulls from owl pellets 250 159. Mound of ground squirrel 252 160. Poisoned ground squirrels 253 161. Cottontail rabbit 255 162. Section of Walmsley rabbit trap 256 163. Walmsley trap set under a fence 256 164. Pocket gopher .258 165. Section of gopher tunnels 258 166. Porcupine . . 259 167. Two-toed sloth ... 260 168. Great anteater 261 169. Armadillo ... . . 261 170. Gorilla „ 262 LIST OE ILLUSTRATIONS XV11 FIGURE PAGE 171. Monkey 263 172. Stomach of ruminant 264 173. African elephant 266 174. American bison 268 175. Alaska moose 270 176. Elk 271 177. Caribou 273 178. Manatee 275 179. Skull of Greenland whale 276 180. Dolphin 276 181. Sperm whale 277 182. Sulphur-bottom whale 277 183. Finback whale 278 184. Humpback whale 278 185. Finback whale 279 186. Whale steamer 279 i860. Whaling station 280 1866. Steamer towing whales 281 187. Head of sulphur-bottom whale 282 188. Raising a side of whalebone into a ship .'.... 283 189. Bundles of whalebone 284 ECONOMIC ZOOLOGY CHAPTER I PROTOZOA The phylum Protozoa includes a large number of small animals; they are mostly of microscopic size, though some of them are easily seen with the naked eye. They all consist of but a single cell, which is sometimes quite complex. The phylum is usually divided into four classes according to the presence or absence of organs of locomotion and the character of these organs, if present. These classes are as follows: I. Rhizopoda, with pseudopodia, Fig. i. II. Mastigophora, with flagella, Fig. 2. III. Sporozoa, non-motile, in adult condition at PIG. i. — Ameba. cv, contractile vacuole; ec, ectosarc; en, endosarc; fv, food vacuole; n, nucleus; p, pseudopodia. Highly magnified. least, Fig. 4. IV. Infusoria, with cilia. Of these classes the first three are of economic importance and will be discussed in turn, the Infusoria are of little importance, though some of them may be con- cerned in certain intestinal diseases. Rhizopoda. — Without further classification several representatives of^this class will now be discussed. Ameba, Fig. i . There are two (possibly more) species of this familiar genus that are found in the human intestine, Ameba or Entameba coli ZOOLOGY and E< histetytiea vr: dyswnleria. Authorities differ as to whether they should be considered as belonging to the genus Ameba or to a distinct genus. E. coliis commonly found in the human intestine; as many as 60 per cent, of the feces examined in one instance, showing this species; it is apparently not pathogenic. E. histolytica is supposed to be the cause of at least one kind of Amebic or Oriental Dysentery; and one of the first warnings one receives in going to the Orient is against eating raw fruits or vegetables unless they have been peeled or have been thoroughly washed. This entameba burrows between the cells of the digestive epithelium or, perhaps, into the cells themselves, by its ameboid activities. (E. buccalis, another species, is found in carious teeth.) Rabies, or hydrophobia, one of the most fatal of the diseases to which man is subject, is transmitted, usually by the bite of a dog or some other animal. It was formerly thought that dogs "went mad" from heat, especially during the "dog days;" from having tin cans tied, by mis- chievous boys, to their tails; and from other causes. It is probable that animals never "go mad;" they become infected with rabies only through the bite of some other animal suffering with the disease. In the nerve cells of the brain and spinal cord of animals suffering from rabies are found, by proper staining methods, minute bodies of variable size known as Negri bodies or neurocytes hydrophobiae, Fig. 5. If not the cause of the disease, as many think, they are, at least, a constant accompaniment of it; and it is now possible by them to tell, by the examination of the brain of the suspected animal, whether the human victim should be given the antirabic treatment or not. Formerly it took from two to three weeks to determine whether an animal were "mad;" now the determination can be made in half an hour, which is obviously a wonderful advantage in deciding whether to administer the Pasteur treatment. Negri regarded the bodies that bear his name as Protozoa, belonging to the class Sporozoa. Other workers declare them to be Rhizopods — the class under discussion. In the skin of persons suffering from smallpox are found small bodies that are considered by many to be Rhizopods and to be the cause of the disease. Possibly still other less well-known diseases may be due to the Rhizopods. PROTOZOA o Foraminifera form an order of the class Rhizopods that is of some economic importance because of the limestone that is formed from the dead calcareous shells or tests, Fig. 6. One of the best known of the foraminifera is Globigerina. This form, which is about the size of a small pin-head, is widely distributed over the ocean, and the shells of the dead animals fall to the sea bottom where they form the so-called Globigerina ooze, that solidifies to form gray chalk. Nummulites are the largest of the foraminifera, sometimes reach- ing the size of a silver dollar, which they resemble somewhat in shape. The pyramids of Egypt are built largely of nummulitic limestone. Radiolaria are an order of Rhizopods having usually a complicated skeleton of silica. They are all marine forms and after death their skeletons settle to the sea floor as radiolarian ooze, sometimes hundreds of feet thick, that forms flint or quartz. Mastigophora. — Of the pathogenic flagel- lata the best known genus is Trypanosoma, of which there are several species, parasitic n -, e . i ~ PIG. 2. — A try panosome ; in all classes of vertebrates up to man. One a parasitic flagellate. of the most terrible diseases to which man is Greatly magnified, subject is trypanosomiasis or sleeping sick- ness, which of late years has been sweeping over Africa and destroying the natives by the hundreds of thousands. It is said to be fatal in 100 per cent, of the cases, tho headway is being made toward discover- ing a cure. The organism concerned is T. Gambiense, Fig. 2, which is introduced into the human blood by the bite of the tsetse fly, Glossina palpalis. Whether the protozoan undergoes a part of its life history in the body of the fly or is merely carried mechanically is a debated question; possibly there may be another and an unknown host; at any rate it has been found that the spread of the disease may be checked by cleaning up the brushy areas along streams and water-courses. Just how the trypanosoma produces its ill effects is uncertain; it may be found in the blood, where it destroys the red cells, and in the cerebrospinal fluid. The disease, which may run its course in -a few months or last for years, exhibits various symptoms, the most evident of which is a marked drowsiness or coma that has given the popular name to the disease; the patient loses all desire for food and gradually 4 ECONOMIC ZOOLOGY wastes away and dies in a terribly emaciated condition, Fig. 3. While it is the natives of Africa that chiefly suffer, the organism attacks whites as well as blacks, and several investigators have sacrificed their lives in studying the disease. One of the most serious and fatal diseases of domestic animal in the Orient is Surra. This disease is probably caused by a Trypanosome introduced into the blood by the bite of a fly. Another serious disease of cattle in this country is Texas fever. The organism here, Babesia, is considered by some workers to be a flagel- late, by others to belong to the next order, the Sporozoa. How the cattle "caught" the disease was a great mystery until Smith and Kilborn discovered that the germ is carried from animal to animal by a tick. The adult female tick is fertilized while hanging PIG. 3. — Victim of sleeping sickness, shortly before death. (After Calkins, Protozoology.) to the skin of the ox; she gorges herself with the infected blood of her host and falls to the ground, where she lays an enormous number of eggs. Each larva, when it hatches, is supplied with a little of the in- fected blood ;*it crawls upon a blade of grass where it will die unless another ox brushes against the grass, when the young tick may suc- ceed in attaching itself to the hair of this ox; here it develops into an adult and infects its new host the first time it feeds upon its blood. No wonder the spread of the disease was so mysterious, when one animal could infect another without ever having been within a hundred miles of it. Sporozoa. — Of these very minute Protozoa the most important, perhaps, is the genus Plasmodium, of which there are probably several PROTOZOA Development of Parasite in Some may be taken into the stomach \ J*_ of the Mosquito when it bites PIG. 4. — Diagram to illustrate the life-history of the malarial parasite; i, is a red blood corpuscle; 2 to 7 show the development of the parasite in the corpuscle; a, b, c, d and a', b', c', d' and e show the development of the parasite in the stomach of the mosquito; /, g, h, i, show the development in the capsule on the outer wall of the stomach of the mosquito; k is the salivary gland of the mosquito. Greatly enlarged. (After Doane, Insects and Disease.) O ECONOMIC ZOOLOGY species. This is the organism that causes one of the oldest and most widely distributed diseases of man, malaria, which was the first disease that was proven to be directly caused by a protozoan parasite. Until near the beginning of the present century both the cause and the mode of transmission of malaria were unknown, though Lancisi, in 1718, ventured the statement that mosquitoes or gnats might introduce certain poisonous substances, found in swampy regions, into the human blood and thus cause malaria. It has been recognized for ages that malaria was more prevalent in damp and swampy regions and the disease owes its name — Mai-aria — to the commonly held idea that it was due to bad air or miasmas found hanging over swamps and such places; it was also generally thought that the disease could be contracted by drinking bad water. In i88iDr. La veran discovered a curious new parasite in the blood of malarial patients, which he claimed was the cause of the disease. This discovery did not attract much attention until some years later when Laveran and Manson independently suggested that the germ might be transmitted to man by the bite of some blood-sucking insect. After years of investigation Major Ronald Ross, of the English army, finally worked out the life history and proved that the insect re- sponsible for the transmission of human malaria is a mosquito belonging to the genus Anopheles, while bird malaria is transmitted by the genus Culex. The life-history of the sporozoan is essentially the same in the three types of the fever, the main difference being the different lengths of the developmental periods, the tertian fever producing the attack or chill every 48 hours, the quartan fever every 72 hours and the pernicious fever every day. The whole life-history in both hosts, man and anopheles, is briefly as follows: the organisms are introduced into the blood when the mosquito bites. These minute, elongated sporozoa move about in the blood plasma and finally enter the red blood cells. According to some authors they do not actually enter the cells, but it is difficult to see how the following processes could take place unless they do. In the blood cells they grow and give off poisons that are contained within the cells. At the end of their developmental period, 48 hours, for example, in the tertian fever, they break down into numerous spores, and it is the escape from the corpuscles of these countless spores, together PROTOZOA 7 with the above mentioned toxins, that causes the chill. This process of sporulation, which continues at very regular intervals, sets free into the blood three types of spores which, for convenience may be termed male, female and neutral. If, now, a culex mosquito sucks the blood containing these spores, they are all digested along with the blood, in the mosquito's stomach; if, however, it be an anopheles, instead of some other genus, that sucks the blood, different results follow. In the anopheles' stomach the neutral forms are digested, along with the blood, but the male and female cells conjugate and form a cyst or nodule in the wall of the stomach. This cyst breaks down into many — perhaps ten thousand — tiny sporozoites, and as there may be hundreds of cysts in one mosquito the number of sporozoites is enormous. After ten days or more these sporozoites collect in the mosquito's salivary glands, where they may live for two or three weeks, during which time, if the mosquito bite a human being she will inject into the wound some of the sporozoites, and the life cycle is begun again in another victim. Several persons may be infected by the same mosquito. It has been found that, under certain conditions, the sporozoon may remain dormant in the spleen or bone marrow for months or years, where it can resist the action of quinine, the universally used specific for malaria; under favorable conditions it may resume its activities and the person will suffer a relapse. Not only has this life-history of the parasite been very carefully worked out, but numerous practical tests have been made that prove very conclusively that malaria is not " caught" from mists, drinking water, etc. For example, wherever malaria is found, excepting sporadic cases that may be introduced from other regions, the anopheles is found. There are sections where this mosquito exists without malaria, simply because nobody has introduced the disease into that region. The reason for the prevalence of malaria in swampy regions is, of course, that it is in such places that mosquitoes abound. The experiments of Grassi, the Italian, will serve as an example of many similar experiments. "In 1900 he received permission from the government to experiment on the employees of a piece of railroad that was being built through a malarial region. This was divided for the purposes of the experiment into three sections, a protected zone in the middle and an unprotected zone at each end. Those working in the protected zone had their houses completely screened and no one was 8 ECONOMIC ZOOLOGY allowed out of doors after sunset except they were protected with veils and gloves. Early in the season they were all given doses of quinine to prevent auto-infection. In the unprotected zones no screens were used and everyone was allowed to go without special protection. The result for the summer was that there were no new cases of fever in the protected zone. In the unprotected zones practically all had the fever as usual." 3. *• to. FIG. 5. — Negri bodies or neurocytes hydrophobias, in different stages of chromatic distribution. Greatly magnified. (From Calkins, Protozoology, after Negri.) Yellow fever, one of the most dreaded of human diseases is now known to be transmitted by the bite of a mosquito, Stegomyia, just as is malaria by Anopheles. While the germ of the disease has not been seen there are reasons for thinking it may be a sporozoon of extremely minute size, so that a brief account of the disease may be in place here. PROTOZOA 9 In 1900, during the American occupation of Cuba, the yellow fever became so prevalent there that a yellow fever commission of medical officers was ordered to study the disease. Dr. Finlay of Havana had claimed that the disease was transmitted by the bite of a mosquito, and the commission decided to prove or disprove this theory. No braver nor more useful piece of work has, perhaps, ever been done than that of the members of this commission — Drs. Reed, Carroll, Lazear and Agramonte. The crucial test was to let an infected mosquito — that is, one that had bitten a yellow fever patient — bite a non-immune person to see if the disease would thus be transmitted. Dr. Carroll allowed himself to be bitten by such a mosquito and in due time developed the disease, so that he was the first person to whom it was proven that the mosquito had carried the disease. His heroism fortunately did not cost him his life, but Dr. Lazear, who was accident- ally bitten, died in a few days. Other volunteers allowed themselves to be experimented upon, and, when the conditions were right, developed the disease. It was found that it is only during the first three days of the disease that a mosquito may be infected by biting a yellow fever patient, and that 12 days must elapse before this mosquito is capable of infecting another person. It is even claimed that the mosquito may transmit the infecting power to her offspring. Various experiments like the one quoted above for malaria were tried with yellow fever. For example, a number of non-immunes lived for three weeks in a mosquito-proof house, where they were supplied with clothing and other articles from a yellow fever hospital. They even slept between soiled sheets from a bed which a yellow fever patient had occupied. None of them developed the disease. When some of these men were later inoculated they developed the disease, showing that they were not immunes. Thus it was conclusively proven that yellow fever is transmitted by the bite of the Stegomyia mosquito and in that way alone. The effect of this discovery upon the health of Havana,, New Orleans, the Canal Zone and other pest-ridden places, is known to all. The problem resolved itself simply into cleaning up the swamps, covering the cisterns, etc., thus exterminating the mosquitoes. The methods employed in this work will be discussed in the section dealing with insects. The terrible mortality among the laborers, engineers, doctors and nurses, while the French were at work upon the Panama Canal, was 10 ECONOMIC ZOOLOGY almost eliminated while the Americans were at work Canal Zone is now as healthy as almost any part of the Another disease that may be caused by a protozoan quite certainly transmitted by one or more species dengue or break-bone fever, common in many parts of is a disease that causes suffering, but seldom death. Kala-azar or dum-dum fever is a very dangerous that is supposed to be due to a protozoan parasite, man by the common bedbug of India. there, and the United States. parasite, and is of mosquito is the tropics. It tropical disease transmitted to FIG. 6. — Tests of foraminifera, magnified about 10 diameters. Protozoology.) (After Calkins, Infusoria. — This well-known and zoologically interesting class of ciliated protozoa, represented by the commonly studied form Para- mecium, is of little economic importance. Infusorial earth, used in making dynamite, is not made up of infusoria, as might be ex- pected, but of the tests of diatoms and other forms. A few of the infusoria may be concerned in some of the intestinal diseases. CHAPTER II PORIFERA The porifera or sponges are plant-like aquatic animals, all but one family of which are marine. The typical or primary form of a sponge is cylindrical or vase shaped, Fig. 7, but in nearly all cases a process of branching has con- verted the simple vase into a highly complex organism or colony. In the simple sponge the central cavity opens to the exterior by a PIG. 7. — A colony of simple sponges. X/£- single, large, excurrent opening or osculum, and by numerous minute inhalent openings or pores, Fig. 7. The pores lead into more or less complicated systems of canals which are lined with vibrating flagella that cause currents of water to flow through the canals into the central cavity and thence out of the osculum. It is these currents of water that supply the organism with food and oxygen, and at the same time 12 ECONOMIC ZOOLOGY remove waste. Between the outer layer of cells, the ectoderm, and the inner layer, the entoderm, is a more or less gelatinous layer, the meso- derm, in which are found the skeletal elements that give the sponge its definite form. In the commercial sponges, of particular interest here, the skeleton consists mainly of a complicated network of horny fibres of a substance called spongin, which is stiff and hard when dry, but is more or less flexible when wet. In other sponges the skeletal elements are tiny structures of various shapes, called spicules, which may be either calcareous or silicious. Sponges multiply asexually by budding and by means of asexual spores or gemmules; and sexually by means of ova and sperm. The fer- tilized ovum develops into a ciliated, free-swimming larva that later becomes attached and develops into the plant-like adult sponge. In the ordinary commercial sponges the process of budding and branching has gone so far that it is difficult to recognize the primary vase-shaped individual in the complicated mass with dozens or hundreds of oscula and thousands of pores. In some of the older texts the sponges were classified under the phylum ccelenterata, but they are now generally placed in a separate phylum. Fossil sponges are found in all geological formations from the Cambrian upward. Although found in all seas and at almost all depths, it is in tropical and subtropical waters they especially abound. "The sponges of commerce come from the eastern Mediterranean Sea, the West Indies, and the coasts of Florida and Central America. In the Grecian Archipeligo, Crete, Cyprus, on the coasts of Asia Minor, Syria, Barbary, and the Bahama Islands, sponge fisheries constitute a very im- portant industry. The finest sponges are obtained in Turkish waters. The fishing season commences in May and closes in September or October. Diving is practised, and is carried on in a rude, primitive manner. The diver, who has no dress, siezes hold of a large stone, to which a line is attached, and sinks by means of it to a depth varying from 30 to 180 (?) feet. Keep- ing hold of the rope, he tears the sponges off the rocks within his reach, and places them in a net; when he secures a netful he signals by means of the rope to be drawn up. "Modern diving dresses have been successfully introduced in some places. The West Indian trade is annually increasing, and the fishing in- dustry gives employment to 500 boats and 2000 persons. The Bahamas and the coast of Florida are the best fishing grounds. PORIFERA 13 "Florida is the only State in the Union which has a sponge-fishery, and there it is confined to the southwestern part of the coast, along the reefs, and to the extensive rocky shoals that lie between St. Mark's and Anclote Keys. The former is known as the Key ground, with its centre at Key West, the latter as the bay ground, with its centre at Tampa Bay. " Nearly all the sponges used in the United States were brought from the Mediterranean till 1852, when attention was called to the immense numbers that were growing in Florida waters. As soon as it was found that the quality of these compared favorably with those of Europe the merchants and fitters-out of vessels of Key West engaged very actively in the business of placing them on the market. At first the best qualities were bought from the fisherman at 10 cents a pound. As Mediterranean sponges became scarce and costly the Florida sponges came more and more into demand, and their value increased proportionately. After about 18 years' fishing on the known ground the supply began to fail. Then, in 1870, a new area of ground, larger than the old one, was discovered, and this gave a new impetus to the trade. In that year Appalachicola sent out a small fleet of sponge vessels which has since been largely increased, and the industry has been energetically pursued with good results. "The methods employed in the fishery differ greatly from those em- ployed in the Mediterranean. Small vessels, carrying crews of from 5 to 15 men, are fitted out for trips of from four to eight weeks on the sponge grounds. The crews are paired off into small rowboats, or 'dingies,' to catch the sponges. One man stands in the stern, skulling the boat, while the other kneels in the bottom amidship, leaning over the side, and scans the bottom of the sea by means of a water-glass. When a sponge is sited the boat is stopped, and the kneeling man uses a three-pronged hook, attached to a slender pole 30 to 50 feet in length, to secure it. Considerable dexterity is required of both men. To cure the sponges they are at first spread about the vessel's deck in their natural upright position so that they will die, and while decomposing allow the softened animal matter to run off freely. When they have been several days in this position they are taken to the shore and thrown into the water in little pens, called "kraals' (corrals), where the re- maining substance is soaked and squeezed out, after which the sponges are removed at intervals and beaten with a stick to facilitate the process. "Although most actively prosecuted during the summer, sponge fishing is now followed more or less throughout the year, the vessels beginning their trips during January and working the different beds successively from north southward. The state of the weather greatly affects the result of the fishery. In some years it has been a complete failure, while in others it has been very profitable, always owing to the weather. As the natural beds of sponges 14 ECONOMIC ZOOLOGY have become scarcer prices have advanced, so that even if a vessel does not secure as large a quantity in a given time as formerly the financial result is about the same. " Several varieties of sponges are caught in Florida waters. They are first, sheep's wool, which sell for $2 to $5 a pound; second, yellow sponges, which sell for 50 to 60 cents a pound; and third, grass sponges, which are coarse in texture and not durable, and sell for 15 to 25 cents per pound. Other coarse grades are boat and glove sponges. When these are marketed they are cleaned of sand and shells, and then pressed into small bales of 100 to 120 pounds each, in which form they go to the wholesale dealers. The yellow sponge especially is subjected to a bleaching process to improve the color, but the process ordinarily employed greatly weakens the fibre. " Owing to the rapidly decreasing supply of the finer grades and the rising price the problem of propagating sponges artificially has been taken up seriously by the United States Bureau of Fisheries. It has been found that sponges may be raised successfully both from the egg and from cuttings but, owing to the much shorter time required for the latter to reach a marketable size, the first method has been abandoned. The technical prob- lems of sponge raising have been largely solved and there is every promise that .their culture on a commercial scale can be undertaken in the near future, and that the depleted grounds will be restocked. "In 1900 the Florida sponge fisheries employed 2225 persons, with 156 vessels and other apparatus valued at $594,598. The product aggregated 418,125 pounds of all kinds of commercial sponges, which sold for $567,685. To this total sheep wool sponges contributed 181,131 pounds, valued at $483,263 "(36). Besides the above, sponges are of economic importance in that the silicious spicules of some species form large flint deposits. Negatively, certain sponges are of economic importance because of their destruc- tiveness to oyster beds, either by smothering the oysters or by boring (certain "Boring Sponges" have this curious power) through their shells and thus destroying them. CHAPTER III C(ELENTERATA This phylum, which by some authors, is made to include the porif era, though important scientifically, is one of the least importance economic- Pic. 8. — Hydrozoa. A, part of a colonial species, Obelia. i, ectoderm; 2, entoderm; 3, mouth; 4, ccelenteron; 5, coenosarc; 6, perisarc; 7, hydrotheca; 8, blastostyle; 9, medusa bud; 10, gonotheca. B, free-swimming medusa of Obelia. i, mouth; 2, tentacles; 3, reproductive organs; 4, radial canals; 5, statocyst. C, larva (planula) of Laomedea. A, Xio; B and C, more enlarged. (From Hegner, College Zoology; A, after Parker and Haswell; B, after Shipley and MacBride; C, after Parker from Allman.) ally. It includes a large number of aquatic forms, mostly marine^ and mostly soft, even jelly-like, in character; they are radially sym. 15 i6 ECONOMIC ZOOLOGY metrical and have a single gastrovascular cavity. Many of them exhibit two stages — the polyp or hydroid form and the medusa or jelly-fish stage. They possess minute sting cells or nematocysts. They are usually divided into three or four classes, as follows: 1. Hydrozoa, Fig. 8, fresh water polyps (Hydra, for example); hydroids (Obelia); small jelly-fish (Gonionemus); and a few stony corals. 2. Scyphozoa, Fig. 9, mostly large jelly-fish, sometimes as large as a wash-tub. 3. Anthozoa or Actinozoa, Fig. 10, flower-like sea anemones, corals, etc. cr A EC FIG. 9. — Three Scyphozoa. Somewhat reduced. A, Tessera princeps. B, Periphylla hyacinthina. C, Charybdea marsupialis. (From Hegner, College Zoology, after Sedgwick and Haeckel.) 4. Ctenophora, Fig. n, comb-jellies or sea walnuts, very transparent jelly-like forms with eight bands of comb-like, radially arranged, ciliated plates or locomotor organs. This class is often described as a distinct phylum. Hydrozoa. — Except for comparatively unimportant sales to colleges and museums this class has practically no economic importance so far as is known; possibly they may help destroy organic waste particles in the water. Scyphozoa. — The same may be said of this class, except that the common jelly-fish or sea nettles are sometimes a pest along bathing beaches on account of the painful effect upon the human skin of their CCELENTERATA sting cells. Indeed, a few forms, for example, among the Cubomedusse, Fig. 9, may produce quite serious results. Anthozoa. — This is the most important of the ccelenterate classes. Two species were formerly, probably still are, eaten in Italy under FIG. 10. — A sea-anemone, Metridium marginatum, partly cut away so as to show its structure. Xi. i, intermediate zone; 2, lip; 3, siphonoglyph; 4, gullet; 5, inner edge of gullet; 6, edge of mesentery; 7, cavity of tentacle; 8, inner ostium; 9, outer ostium; 10, primary mesentery; n, muscle band on primary mesentery; 12, abnormal tertiary mesentery; 13, secondary mesentery; 14, tertiary mesentery; 15, quaternary mesentery; 16, reproductive gland; 17, mesenterial filament; 18, opening for mesenterial filament. (From Hegner, College Zoology, redrawn from Linville and Kelly.) the name "Ogliole." The corals are the most important of the cce- lenterates. They have practically the structure of the sea anemones but secrete at their attachment a limestone base that forms the well- known coral reefs, so dangerous to shipping in many parts of the tropics. 2 i8 ECONOMIC ZOOLOGY Occasionally, these reefs take a circular form and may form a ring-like island or atoll, Fig. 12, with an enclosed lagoon; there have been several theories to explain the formation of atolls. In many parts of the Pacific Ocean, large groups of islands, have been formed through the action of the coral polyps, and, in many places, large deposits of limestone rock owe their origin to these small animals. The only corals that have any value as such, except for scientific purposes, are the so-called "precious corals;" they are usually of a C.SS. FIG. ii. — Ctenophora. Somewhat enlarged. A, Hormiphora plumosa; side view, i, mouth; 2, aboral pole with sense organ; 3, funnel; 4, paragastric canal; 5, a ciliated band; 6, canal; 7, tentacular pouch; 8, tentacle; 9, gelatinous substance. B, Pleurobranchia pileus; view of aboral aspect, showing central statocyst, polar fields (Pf), and 8 ciliated bands (c.ss, c.tr). (From Hegner, College Zoology, A, from Shipley and MacBride, after Chun; B, after Lankester.) bright red or pink color and are made into necklaces and other orna- ments. These corals are of a delicate branching type and are collected mainly in the Mediterranean Sea, especially along the coasts of Africa, Italy, Sardinia, and elsewhere, even as far as the Cape Verde Islands. They were formerly thought to have medicinal value and to be able to ward off danger and are still worn by superstitious Italians to keep off the "evil eye." Precious coral has been used in these ways since remote times; CCELENTERATA . 1 9 the Gauls ornamented their weapons with the material until the oriental demand became so great as to use up the entire supply. A cheap variety of precious coral is collected in Japan; it is also found off the coasts of Ireland and Australia. There is a black coral dredged in the Persian Gulf. The African fisheries have changed hands several times but are now under French control, so that non-French dredgers have to pay a heavy royalty. Previous to the French Revolution, Marseilles was the chief centre for collecting and work- ing the coral; now Naples, Genoa and Rome are the chief centres. FIG. 12. — A small atol. A sketch of Whitsunday Island in the South Pacific- (From Hegner, College Zoology, after Sedgwick and Darwin.) The Algerian reefs are divided into 10 regions, only one of which is dredged each year, 10 years being considered time enough to allow the beds to recuperate. They are dredged in waters from 25 to 1000 feet, though mostly in the shallower depths. The value varies according to color, size and current demand, the last fluctuating greatly with the changes of fashion. The finest tints may bring $400 to $600 per ounce. Ordinary reds in small pieces, $10 per ounce. Fine pieces called " collette, " used for children's necklaces, etc., bring $i per ounce. Very large pieces are much in demand in China for the official buttons of the mandarins. CHAPTER IV ECHINODERMATA This phylum consists of a number of well-known forms all of which are marine and most of which are very slow in their motions. As their name indicates they are the "spiny-skinned" animals, though the spininess varies greatly in different species. They are radially sym- metrical and were, therefore, by earlier writers classed with the Coelenterates as "Radiata." Their radiate structure is usually built on a plan of five, and their organs of locomotion, in most cases, consist of small sucker-like tube feet, controlled by a characteristic system of water tubes known as the water-vascular system. Unlike the ccelenterates they have a well-developed coelom and possess the three cell layers characteristic of the higher animals. An anus, distinct from the mouth, is generally present. There are many extinct groups of echinoderms that, as fossils, are interesting and important geologically. The living representatives of this phylum are usually divided into five classes, three of which are of some, though not of very great, economic importance, the other two classes are of scientific interest only. I. Asteroidea, Fig. 13. As their name indicates these are the starfishes, the most familiar of the echinoderms. They are typically five-rayed, the rays meeting in an indefinite central disk. On the upper or aboral side is a generally distinct madreporic plate, on the lower or oral side is seen the centrally located mouth, radiating from which are the five ambulacral grooves, filled with tube feet. II. Echinoidea, Fig. 14, the sea urchins. The pentanerous ar- rangement is not so obvious here as in the preceding class since there are no radiating arms. The calcareous plates are united into a more or less globular shell or test, Fig. 15, covered with movable spines (hence the name, hedgehog), and perforated with five radiating sets of holes for exit of the long, slender tube feet. The plates that bear. 20 ECHINODERMATA 21 the perforations form the ambulacra! areas, the plates between these five areas form the interambulacral areas. The mouth is in the centre of a membranous peristome and is usually provided with a complicated jaw apparatus known as Aristotle's lantern. III. Holothuroidea, Fig. 16, sea cucumbers. As the popular name indicates these animals, especially certain species, are distinctly FIG. 13. — Starfish. xK- cucumber-like, having an elongated, spindle form, 'with the anus at one end and the mouth, surrounded by branching ^tentacles at the other. The bony skeleton here consists of small variously shaped plates, usually in such small quantity that the body wall has a soft leathery texture. 22 ECONOMIC ZOOLOGY IV. Ophiuroidea, Fig. 17. These are the brittle-stars or serpent- stars; the first name is appropriate because of the brittle, delicate character of the rays; the latter name comes, as the class name indicates, from the snake-like character of the rays. The distinct central disk and snake-like arms are sufficient to identify the members of the class, Fig. 17. In some species the rays are much branched, making the FIG. 14. — Sea-urchin. xM- animal very complex in appearance, as in the basket fish or Venus' basket. V. Crinoidea, Fig. 18. These are the feather-stars, sea-lilies, or stone-lilies, named from their feather or plant-like appearance. They have five arms which often branch repeatedly and give the feathery appearance. They are generally attached by the aboral apex, either during their developmental stages or throughout life, sometimes by a ECHINODERMATA FIG. 15. — Test of sea-urchin, with spines removed. XL A B FIG. 16. — A sea-cucumber, Thyone briareus, partly buried in the mud. (From Hegner, College Zoology, after Pearse.) ECONOMIC ZOOLOGY long flexible stem, made up of disk-like segments. They occur at all, though mostly moderate, depths; many are known only as fossils, their calcareous skeletons helping to form extensive limestone deposits. The Asteroidea are of very considerable negative importance since they are a serious menace to the shellfish industry, especially to oysters. A single starfish, in captivity, is said to have eaten 20 clams in six days, and since along the northern coasts the starfish are often extremely abundant, they sometimes are very destructive to FIG. 17. — Serpent or brittle-star. Xi. oyster beds. The method of getting rid of them will be discussed under the head of oyster culture. The Echinoidea, under the name of sea-eggs, are of some, though not very great, economic importance. In the West Indies, Italy and in the far east they are largely eaten, both raw and cooked, especially when they are sexually mature and full of eggs, as it is the eggs that are eaten. A large sea-urchin just before spawning contains a very considerable quantity of roe. A decade or more ago at Barbados, the centre of the sea-egg industry, the annual business was worth about $20,000. The Holothurians are the most important, economically, of the ECHINODERMATA 25 echinoderms. Several dozen species are used as food, especially by the Chinese, and other orientals, under the name trepang; they are also called b$che-de-mer. Some species bring very high prices, others seem less desirable. The animals, some of which may reach a length of two feet, are eviscerated, the leathery walls are then boiled, soaked in fresh water, smoked, and dried. The result is an irregular mass of rubber-like substance which can be transported easily and is made into soup and other articles of diet, which are said to be very palatable. FIG. 1 8. — A crinoid, Pentacrinus madearanus. Xi. Only a part of the stem shown. (From Hegner, College Zoology, after Cambridge Natural History, from Thompson.) Trepang is prepared by the Chinese of California and Hawaii, but the chief centres are in the Orient; for example 600 tons annu- ally are collected from the north coast of Australia, and the annual trade amounts to hundreds of thousands of dollars. Considerable quantities are also collected in the West Indies. The Ophiuroidea have practically no economic importance and the same is true for the Crinoidea except for their aid in forming lime- stone beds and in enabling geologists to determine geological horizons. CHAPTER V PLATYHELMINTHES. FLAT-WORMS In older texts the group name "Vermes" was used to include all of the worms. In modern books the worms are usually placed in three or more phyla — the Platyhelminthes or flat-worms, the Nemathelminthes or round- worms, the Annulata or segmented- worms; and sometimes the curious little worm-like rotifers are placed in a phylum of their own, though they and some other worms are of uncertain affinities. The first three of these groups will be taken up in order, as each has considerable economic importance. The flat-worms, though a lowly group, are more highly specialized than the ccelenterates. They have three .germ layers, the mesoderm forming important systems of organs — muscles, urogenital organs, etc. They are bilaterally instead of radially symmetrical and, as the FIG. i9.-Planaria. A common name indicates are of a distinctly fresh- water flat-worm. X5- J flattened form. Their internal structures are difficult to make out in the laboratory, and vary con- siderably in different species, being highly degenerate in some parasitic forms. The flat- worms are usually divided into the three following classes : I. Turbellaria, Fig. 19, free living forms with ciliated ectoderm; found in fresh and salt water, rarely on land. Represented by the familiar genus Planaria of our ponds and pools. II. Cestoda, Fig. 20, long, much flattened forms divided into numerous (sometimes many hundred) more or less independent segments, no alimentary canal present; parasitic in habits. Repre- sented by the common tapeworms. III. Trematoda, Fig. 21, usually short and broadly flattened, with ventral suckers and much branched digestive and reproductive organs. Parasitic in habits. Represented by the liver and other flukes. 26 PLATYHELMINTHES. FLAT-WORMS 27 Since the Turbellaria have little if any economic importance they will not be further discussed. The Cestodes or tapeworms, Fig. 20, are found in the digestive tracts of vertebrates. Naturally those found in man are of the most interest and importance. There are at least two large tapeworms parasitic in man: Tania saginata, the unarmed, beef, or fat tapeworm, the commonest form, and T. solium or pork tapeworm. The former is taken into the body by eating imperfectly cooked beef; the latter by eating imperfectly cooked pork. The latter is the more dangerous but, according to Osier, is very rare in the U. S. The former is found practically everywhere and though unpleasant is not necessarily very serious. The life-history of T. saginata is briefly as follows: the adult worm lives in the intestine of man; usually only one worm is found in an individual, but as many as 59 have been reported. The worm has a small head, about 2 mm. in diameter, Fig. 20, B, with four suckers but without the circle of hooks that is found in T. solium and that is shown in the figure. Following the head or scolex is a slender neck, the segments of which gradually enlarge toward the posterior end until, in the main body of the animal, they may be i cm. wide and 2 or 3 cm. long. There may be 1000 or more segments or proglottids in a large worm, totaling a length of 20 or 30 feet. Each of the pos- terior segments is a complete animal sexually, and they are con- stantly breaking off and passing to the exterior with the feces. In ridding a patient of tapeworm by the use of purgatives it is necessary to cause the extrusion of the entire worm, for if the scolex remain attached to the intestine the segments will be rapidly re- generated, at the rate, perhaps, of a dozen a day, so that the worm will soon regain its normal size. It is estimated that a single worm may produce 150,000,000 eggs per year; these, together with entire proglottids, are passed to the exterior and may be taken into the digestive tract of a beef with grass or in drinking water. While still in the proglottids the eggs are fertilized and develop into tiny embryos. These embryos if taken into the intestine of a beef burst out of their containing shells, bur- row through the digestive walls of their second host and become encysted, as tiny bladder-shaped worms known as cysticerci, or bladder worms, in the muscles, especially in the tongue and chewing 28 ECONOMIC ZOOLOGY muscles. If, now, this muscular tissue be eaten, imperfectly cooked, by man, the cysticerci, when the meat is digested complete their development into the adult T. saginata in the intestine of the new victim. Taenia is most common in women especially between 20 to 40 years, and a worm may live for years, if not expelled by proper treatment. Of course, if no raw or very rare beef be eaten it is im- possible to be infected; probably most infections come from pri- vately killed cattle, as the larger slaughter houses keep the beef in cold FIG. 20. — Human tapeworm, Tcenia solium. A, the entire animal. X /4- B, the head or scolex, sc, enlarged; n, neck region; p, segment or proglottid; s, suckers; sc, scolex; gp, genital pore; h, hooks. storage for three weeks, which is thought to destroy the cysticerci that may be present. Thorough salting will also kill the cysticerci. The life-history of T. solium, which most books describe as the "common" tapeworm, is essentially the same as that of T. saginata except that the hog is the second host. The head here is very tiny, not so large as the head of a pin, and is armed with hooks, hence the name "armed" tape worm. The cysticercus of T. solium is not so easily killed by cold storage as that of T. saginata, so that there is always danger from eating raw pork, though the greatest danger is from another worm, to be described later. PLATYHELMINTHES. FLAT-WORMS T. solium is a more dangerous parasite from the possibility of the occurrence of cysticerci in man, forming vesicles known as hydatids, which may cause death. These hydatids are embryos that, in certain cases, develop in the intestine where they were born and then migrate into the muscles of the first host. The Trematodes, Fig. 21, are represented by the liver, lung, intestinal and venal flukes of man and other animals, the disease being known, in a general way as Distomiasis, from Distoma, the generic name of the common flukes. According to Osier there are six species of liver flukes known in man. One of these is extremely common in some parts of the Orient and has occasionally been found in the United States. The patient may die after many years of illness. One of the commonest of the flukes is Distomum hepaticum, living in the bile ducts of sheep and other herbivorous animals. It is found the world over and sometimes causes severe loss among flocks from liver rot. Since a single fluke is said to produce 500,000 eggs and since there may be 200 adult flukes in a single sheep, it would seem that the disease should be ex- tremely common, but the life-history, as will be presently seen, is so complicated that the mortality is enormous and but few eggs ever produce adult flukes. The life-history of the sheep fluke is, briefly, as follows: The fertilized egg is deposited by the • *• genit^! pore; J m, mouth; s, ven- hermaphroditic adult in the bile ducts of the sheep, trai suckers, whence it passes to the intestine and thence to the exterior with the excrement. If the ovum chance to get into water at the right temperature it develops into a ciliated larva known as a miracidium. In swimming about, if this larva come in contact, within a few hours, with a fresh water snail of a certain species it burrows into the soft tissue of the mollusc where, in about two weeks, it develops into the next stage, the sac-like sporocyst. The sporocyst gives rise to several redia, of which there may be one or more generations, the final generation becoming the tailed cercaria. The cercaria leaves the body of the snail and after swimming about for a time forms a cyst on a blade of grass. If this blade of grass be eaten by a sheep FIG. 21. — Liver fluke, Fasciola hepatica. Xi. 30 ECONOMIC ZOOLOGY the larva escapes from the cyst, makes its way from the intestine into the bile ducts where it assumes the adult condition. It will be seen that the chances for an egg to meet all of these unusual conditions are very slight; hence the enormous number of eggs produced by each adult fluke. CHAPTER VI NEMATHELMINTHES. ROUND-WORMS These are the round or thread-worms, which are characterized by their long, slender, cylindrical bodies that are entirely devoid of internal or external segmentation. Their internal structure is usually moderately simple, as might, perhaps, be expected of a group, many members of which are parasitic. Some of them are of microscopic size; others reach a length of a meter. Their chief if not only claim to economic importance lies in their parasitic habits. FIG. 22. — Parts of Ascaris lumbricoides. a,-b, and c, enlarged; d, highly magnified a, posterior end of a male with two penial setae (Sp); b, anterior end from the dorsal side, showing the dorsal lip with its two papillae; c, the same from the ventral side with the two lateral ventral lips and the excretory pore (P) ; d, egg with external membrane of small clear spherules. (From Hegner, College Zoology, after Sedgwick, from Leuckart.) One of the larger and more common of the round-worms is the genus Ascaris, Figs. 22, 23 and 24, found as a parasite in the intestine of man, horses and pigs. It is a brownish worm, about 6 mm. in diameter and from 12 to 30 cm. long, the female being usually some- what the larger; the main features of its anatomy are illustrated by the accompanying figures. The species common to man is A. lumbricoides, the human eel worm. It is one of the most common of the human worm parasites, being frequently found in children from 5 to 10 years of age, and in women more often than in men. It is also more common in warm than in cold climates, and is more frequently 31 32 ECONOMIC ZOOLOGY met with in the country (where sewage disposal is often crude) than in cities. There are usually from one to half a dozen worms in one patient, but as many as 600 in one person have been reported. They may merely cause diarrhea and other discomforts or they may be fatal. The condition may be identified by finding the worms or their eggs in the patients' stools. The history is simple, no second host being necessary. The eggs that are passed out of the body in the feces may be taken into the digestive tract of the same or of another person in drinking water, upon unwashed fruits, vegetables or salads, talk esc. ovt v.v tct FIG. 23. — Transverse section of Ascaris lumbricoides. X 15 cu, cuticle; dl, dorsal line, der. epthm, epidermis; ex.v, excretory tube; int, intestine; lot. I, lateral line; m, muscular layer; ovy, ovary; ut, uterus; v.v.t ventral line. (From Hegner, College Zoology, after Parker and Haswell, from Vogt and Yung.) or by simply eating with dirty hands; possibly the eggs may be carried to man's food or water by flies. It is thus easy to understand how young children may be infected and why women, who generally handle the raw fruits and vegetables, are more subject to the disease than men. Also how bad sewage may spread the eggs. After entrance into the body it takes from one to several months for the eggs to develop into the adult worms. Santonin and calomel are the usual drugs used to rid the intestine of the eel worm. NEMATHELMINTHES. ROUND- WORMS 33 Hookworm. — Probably the most widespread and important worm parasite of man is the now popularly known hookworm, of which there are two chief forms, the European, Ankylostoma duodenale, and the American, Necator ameri- canus. The disease caused by this worm is generally known as hookworm disease, or tech- nically as uncinariasis or ankylostomiasis. The parasites occur in most parts of the world and practically all tropical countries show the presence of the disease, often in a large per- centage of the population; for example 90 per cent, of the people of Porto Rico formerly were infected. While typical of the tropics, the dis- ease is often common in the temperate zones. / In the southern states of the Union the disease is very prevalent; especially among the poorer 4<__M classes. The disease has tbeen recognized in tropical countries for three centuries, though its cause was not discovered until past the middle of the nineteenth century. The first case in the United States was reported in Philadelphia in 1893. Those who live, or have travelled in the southern states are familiar with the so-called "poor whites" of that region. It has been estimated that, at least until a few years ago, there were some 2,000,000 of these unfortunates. They were formerly considered to be a sort of degenerate race, too lazy or stupid or both to work, who eked out a miserable existence on their pitiful little plantations. These people are pale and anaemic and often thin to emacia- tion; the children are stunted physically and FIG. 24. — A female Ascaris lumbricoides cut open to show internal structures. x%. I, pharynx; 2, intes- tine; 3, ovary;' 4, uterus; 5, vagina; 6, genital pore; 7, excretory tube; 8, excretory pore. (From Hegner, College Zoology, after Shipley and MacBride.) 3 34 ECONOMIC ZOOLOGY deficient mentally; many are tuberculous. One of the curious and disgusting characteristics of these people, at times, is the habit of eating dirt, wood, hair, clothing, etc., although the victim usually will deny the habit. About the beginning of the present century Dr. C. W. Stiles, a zoologist, then in the Bureau of Animal Industry, now in the Marine Hospital Service, knowing the effect of hookworm upon the lower animals, made the prediction that it would be found that the condition of these supposedly lazy "poor whites" of the south was due to their being infected with hookworm. The newspapers made great sport of Dr. Stiles' "lazy germ" but the prediction was very soon fulfilled, FIG. 25. — Hookworm, Necator americanus. A, male; B, female. Xio. (After V. L. Kellogg and Doane, Economic Zoology and Entomology, from Wilder.) and we now know that these "poor whites" are not degenerates but are sufferers from a serious, though usually easily cured, disease, named from the worm that is its cause. The worm, Fig. 25, is a small nematode about i cm. in length and about the diameter and color of a very dirty piece of sewing cotton. The male may be easily distinguished from the female by the flaring, fin-like posterior extremity. At the anterior end is the tiny mouth, armed with sharp teeth for puncturing the soft mucosa of the digestive tract; it is in the jejunum that they are chiefly found. They vary in number, in a single individual, from about a dozen to over 4000; but the severity of the attack is not always in proportion to the number of worms found, death having resulted with the former number of worms and recovery with a latter number. They may live in the intestine for five or six years, or even longer. The complete NEMATHELMINTHES. ROUND-WORMS 35 life cycle of the worm cannot take place in the single person, so that the number of worms in the intestine can be increased only by a new infection. The female worm produces the eggs, which are about 35X70 micra (Kooo mm.) in size, in enormous numbers and they pass to the ex- terior with the feces, as many as 4,000,000 it is estimated, with one stool. Desiccation, direct sunlight, too much water and, generally, freezing will kill these eggs, which have usually begun to segment when passed out with the stool. The rapidity of development depends upon the temperature and moisture, but the larvae become infective in four or five days; under favorable conditions these larvae may live for months. Infection may take place either by the mouth or, more commonly, through the skin. It is the entrance of the tiny larvae through the skin, more often of the feet, but of any part of the body, that causes the ir- ritation known as " ground itch," "foot itch," "dew itch," etc. A large percentage of hookworm disease histories show cases of ground itch. The mode of entry through the skin was discovered in 1898 by Looss in a very interesting way. While experimenting with hook- worm larvae he spilled some of them on his hand; he noticed a burning sensation and in a few minutes the larvae had disappeared. After the proper interval, about two months, he found himself suffering with the hookworm disease. To determine what had become of the larvae that were spilled on his hand he poured some larvae on the leg that was about to be amputated from a boy; on sectioning the skin of this leg, after amputation, he found the larvae had worked their way through the skin by way of the hair follicles, sweat ducts, etc. To follow the further course of the larvae he placed some of them on the skin of a number of dogs which were killed and examined at various intervals. In this way he worked out the entire course of the larvae from the skin to their final resting place in the intestine, which is"as follows: after passing through the skin they enter the subcu- taneous blood vessels and are carried by the blood current to the heart; thence to the lung capillaries, from which they burrow through the tissues into the lung alveoli, thence they work their way up the trachea to'the oesophagus, down which they pass to the stomach and intes- tine. It is the tiny lesions made by the larvae in passing through 36 ECONOMIC ZOOLOGY the lung tissue that cause the patient to be unusually susceptible to tuberculosis. The question will be asked — "How can a comparatively small number of tiny worms cause such a marked anaemia in a full grown human being?" The worms cause their serious effects in two or three ways. The amount of blood actually consumed by them is, perhaps not very serious, but it is supposed that they secrete a substance from glands in the head that prevent clotting of the blood, so that as they move from place to place in the intestine the tiny wounds they leave continue to bleed for some time. Again it is stated by some, that another substance is secreted by the worm that prevents the formation of new corpuscles to replace those that are lost. If both of these substances were at work at the same time the results might be most serious. Still another result of their work is seen in the numerous small sores or ulcers left in the mucosa of the intestine by the bites of the worms. These lesions give many possible points of bacterial infection. One hopeful aspect of the disease is the usually easy cure, by the use of two cheap drugs, Thymol and Epsom Salts. They should not be taken without the advice of a physician, and should not be used along with alcohol nor any sort of oil, as the results might be very serious or even fatal. It is, of course, chiefly through soil pollution that the disease is spread. Negroes in the south are almost all infected with hookworm, but for some reason, probably from having been infected through long generations in Africa, they are not seriously affected by the parasite and hence are not apt to subject themselves to treatment. As they are notoriously indifferent to sanitary laws, they probably are the chief instruments in the spread of the disease and are the greatest problem in its attempted control. The Rockefeller Hookworm Commission is endeavoring by a campaign of education and wholesale medical treat- ment to eradicate this curse of the south, which if accomplished will go far toward solving many of the economic problems of that region. What treatment and sanitation can accomplish is shown by the change in conditions in the great Bilibid prison in Manila, P. I. " When the Americans took charge of Bilibid prison the death rate was 238 per 1000 per year; by improving the sanitary conditions this death rate was reduced to about 75 per 1000; here it remained stationary until it was discovered that a very high percentage of the prisoners NEMATHELMINTHES. ROUND-WORMS 37 were infected with hookworms and other intestinal parasites; then a systematic campaign was inaugurated to expel these worms, and when this was done the death rate fell to 13.5 per 1000." Trichinella (Trichina) spiralis, Fig. 26, is a small nematode the adult male of which is about 1.5 mm. in length and a female % mm. Both sexes are enlarged somewhat toward the posterior end, where, in the male, are two short, conical protuberances. The adults are found in the intestine of man and other animals. The female worm produces a large number of embryos, perhaps 10,000 or more, which immediately begin to migrate into the surrounding tissues, finally finding their way, perhaps through the blood and lymph streams, to the muscles of their host where they grow until nearly i mm. in length. As it grows the embryo coils itself into a spiral, FIG. 26. — Trichinella spiralis encysted among muscle fibres. Highly magnified. (From Hegner, College Zoology, after Shipley and MacBride, from Leuckart.) and forms an elliptical cyst around itself as it lies in the connective tissue between the voluntary muscle fibres. It has been estimated that there were from 5,000,000 to 100,000,000, cysts in the bodies of persons who have died of the disease. This cyst, after seven or eight months, begins to degenerate and becomes calcified, and the worm is de- stroyed, though it may take from 2 to 10 years. The adults get into the human intestine from eating uncooked pork in which there are cysts. The cysts dissolve in our intestine, thus liberating the worms which in five or six days are able to produce embryos, and this they may continue to do for a month, if the adults are not gotten rid of by purgatives or by diarrhea; in any case the adult worms usually disappear in five or six weeks. Just how the hog becomes infected is uncertain, probably by eating infected offal, or infected rats; certainly the hog seldom has the opportunity of eating human flesh with or without the trichinella cysts. If the disease, Trichiniasis, be recognized before the embryos have 3 ECONOMIC ZOOLOGY begun to migrate it may be arrested by use of calomel and other purgatives, but after the worms are in the muscles there is no treatment that will affect them. The death-rate has varied in different outbreaks from i to 30 per cent. In America the disease is comparatively rare and is largely con- fined to foreign-born people who make a practice of eating raw ham, sausage, etc. In certain German States where this practice is very common the disease is proportionately more prevalent. As a sure preventive it is simply necessary to thoroughly cook all pork. It is said that the centre of a large piece of fairly well cqoked pork may con- tain live cysts and that salting does not always kill them. Pork from private slaughter houses is more apt to be infected. The fact that pork is marked "U. S. Inspected" does not guarantee it to be free from trichinella. Filaria is a genus of small (less than i mm.) round-worms causing, in man, various diseases. One curious fact about certain species is that they are found in the human blood at night but not during the day, or at least in very much smaller numbers. In a case where a patient reversed his habits and slept during the day the parasites also reversed their habits and were found during the day. How the parasites enter the blood is not certain, probably by the bite of a mosquito, possibly through drinking water. It is often very common in the tropics. One of the diseases probably due, at least in some cases, to this parasite is elephantiasis, which causes enormous and incurable enlargements of the limbs and other parts of the body. There seems to be no drug that will destroy this parasite in the blood. Guinea-worm (Dracunculus) is one of the largest of the round- worms, reaching a length of nearly a meter. The larvae live in a water flea, Cyclops, and probably gain access to the human digestive tract in drinking water. Here they mature and the male dies and is voided. The female, after being impregnated, leaves the intestine and becomes fully developed in the subcutaneous tissue. She contains large numbers of embryos and to get these to the exterior she migrates downward into the leg, usually reaching the foot, where the head punctures the skin, forming a small vesicle which ruptures and allows the embryos to escape. The worm may then leave the body spontaneously or it may be carefully withdrawn, care being taken not to rupture it. It is sometimes the custom to wind the extruded end on a small stick NEMATHELMINTHES. ROUND-WORMS 39 to prevent the worm from withdrawing into the body, each day a little more of the worm is wound on the stick until it is all out of the skin. It may also be removed by surgery or may be killed by injections of bichloride of mercury. Pinworm, whipworm and various other small nematodes are some- times parasitic in the human digestive tract. CHAPTER VII ANNULATA, SEGMENTED WORMS The Annulata or Annelids are those worms in which the elongated, usually more or less cylindrical, body is externally divided into a number of rings representing the internal division into a series of more or less similar somites or metameres. There is usually an ex- tensive ccelom and a complicated system of blood vessels. The nervous system usually consists of a dorsally located brain or cerebral gan- glion in the anterior region, connected around the digestive tract to a ventral nerve cord which usually has a series of ganglia corresponding to the somites. The excretory organs are paired nephridia, which are coiled tubes, usually one pair for each somite, connecting the ccelom with the exterior. The annelids are variously classified by different authors; the two most important classes and the only two of serious economic importance are the Chaetopoda, represented by the earthworms and the Hirudinea or leeches. Earthworms. — There are some 800 species of earthworms, about 90 of which are found in North America. There are about a dozen species of the common Lumbricus and Allolobophora. There are several from South Africa and Australia that are described as being iJ/£ meters in length. They are found everywhere except in frozen latitudes and al- titudes and in dry sandy regions. They generally burrow below frost in winter though some are said to survive freezing. According to the operator of a large steam-shovel they are sometimes found 18 or 20 feet below the surface of the ground. They feed on almost any kind of organic matter, a considerable portion of which they obtain from earth that is passed through the body. This earth from which the food has been extracted is deposited at night around the openings of their burrows as fine pellets known as castings. The amount brought up each night by each worm is so considerable as to 40 ANNULATA, SEGMENTED WORMS 41 interfere with the course ,of the golf balls on the putting greens of golf courses. To rid these greens of this annoyance they are sometimes sprinkled with a lime-and-sulphur mixture or some other poison that is harmless to grass. As soon as the liquid soaks into the ground the worms begin to wriggle out of their unseen burrows so that they may be picked up and destroyed. To illustrate the abundance of earth- worms in the soil, the writer once collected, in this way, over one hun- dred worms, big and little, from a square yard of green. This habit of bringing the subsoil to the surface is most important to the growth of vegetation, the burrows make the soil porous, thus allowing air and mois- ture to penetrate the earth and making it easier for roots to work through the soil, and the castings are constantly building up a finely divided surface at the rate, according to Darwin, of about one-fifth of an inch each year, so that in a generation a rocky field may have all of its stones buried out of sight. The intestinal secretions mixed with these castings are probably beneficial to the soil. FIG. 27. — Medicinal leech, Hirudo medicinalis. X%. The larger sucker is at the . posterior end. Darwin remarks upon the fact that long before the plow was in- vented, even in the form of a crooked stick, the earthworms were con- tinually turning up the soil in this way. Although they may some- times do some damage to young and tender plants, earthworms are evidently of immense benefit to man. Certain laboratory experiments, also, have shown them to be of undoubted benefit to plants. It is also said that earthworms may be and actually are used as food, though they will probably never be popular among civilized peoples. On the other hand they may occasionally be a source of infection in certain diseases by burrowing in the carcasses of buried animals and bringing the germs to the surface where they may infect other animals. They are thought to convey the germs of gapes, a disease of chicks caused by a small worm parasite. -••8 .-V-12 FIG. 270. — Diagram of the internal organs of the leech. i, head with eye-spots; 2, mus- cular pharynx; 3, ist diverti- culum of crop; 4, nth diver- ticulum of crop; 5, stomach; 6, rectum; 7, anus; 8, cerebral ganglia; 9, ventral nerve cord; 10, nephridium; n, lateral blood vessel; 12, testis; 13, vas deferens; 14, prostate gland; 15, penis; 16, ovary; 17, uterus. (From Hegner, College Zoology, after Shipley and MacBride.) ECONOMIC ZOOLOGY Leeches, Fig. 27.— The leeches, of which the genus Hirudo may be taken as an example, are somewhat flattened annelids, with a large posterior and a smaller anterior sucker; the mouth is in the centre of the latter and may or may not be armed with jaws or teeth. Only the digestive system will be noted here. It consists of a short pharynx into which open certain glands whose secretion is to keep the blood, on which the animal feeds, from clotting. The pharynx, Fig. 270, 2, opens into an enormous crop, 3, 4, with about n pairs of lateral pouches for the storage of enough blood to last, perhaps, for many months, as the leech may have very infrequent opportunities for feeding. Back of the crop are a small stomach, 5, and intestine, 6, opening to the exterior through a dorsally located anus, 7. The leech is admirably adapted to its peculiar parasitic mode of life. Its suckers enable it to quickly attach itself to a passing ani- mal, mammal, turtle, fish, etc., its mouth enables it to extract blood from its host without pain to the host, its glands keep the blood from clotting, and its huge crop enables it to store up a very large quantity of blood at each of its probably infrequent feeding times. This power of extracting a considerable quantity of blood, in a painless manner, has given the medicinal leech, Hirudo medi- cinalis, its value to man. In the case of bruises and certain other pathologic condi- tions it is merely necessary to apply a hungry leech — they may be 12 to 15 cm. long — to the desired spot and it will pain- lessly gorge itself with blood and then drop ANNULATA, SEGMENTED WORMS 43 off. So common was leeching in olden times that doctors were often called "leeches." Although not so commonly used in medicine at the present time leeches are used in some cases to remove small quantities of blood from a tender or sensitive region. It is also said that leeches may be used for food, but, like earthworms, they are not likely to be- come popular articles of diet. The other representatives of the An- nulata, though of great scientific interest and importance, have prac- tically no economic importance except as scientific specimens. CHAPTER VIII MOLLUSCA The mollusca are soft bodied (mollis, soft) animals, usually with an external shell or an internal "pen" or bone, found both on land and in fresh and salt water. They are primitively bilaterally symmetrical, but this symmetry is often obscured in the adults. They are unseg- mented. Although the various classes seem at first glance, very dissimilar, yet they have certain structures in common and they have a similar mode of development. Two characteristic organs of the PIG. 28. — Fresh-water mussel, Anodon. XM- /» foot, protruded; g, line of growth, only a few of which have been drawn; ds, dorsal siphon; Ig, hinge liga- ment; u, umbo. phylum are the foot, variously modified for different uses, and the mantle, inclosing between it and the main body the mantle cavity into which the digestive and urogenital organs open. The characters, mainly of the foot, mantle, shell, gills and nervous system, determine the classification of the phylum, which is one of great economic importance. Five classes are usually described. i. Lamellibranchiata or Pelecypoda, Fig. 28. The bivalves, such as oysters, clams, mussels, etc. Usually bilaterally symmetrical. 44 MOLLUSCA 45 the shell consisting of two more or less similar valves and the mantle of symmetrical lobes. 2. Gastropoda, Fig. 43. — These molluscs have usually a single, spirally coiled shell, and are not bilaterally symmetrical. They are the snails, slugs, etc. 3. Cephalopoda, Figs. 46 and 460. Bilaterally symmetrical animals with the foot divided into arms which are provided with sucking disks. Well-developed nervous system concentrated in' the head. Usually with a spiral external shell or with an elongated internal bone or pen. Ink sac usually present. The squids, cuttlefishes, octopi, and nautili. 4. Amphineura, Fig. 47. Bilaterally symmetrical forms often cov- ered with eight transverse calcareous plates. Typically represented by the chitons. 5. Scaphopoda, Fig. 48. A small group of small marine forms whose tubular mantle secretes a slightly curved, conical shell open at both ends. From the shape of the white shell they are called the elephants' tusk shells or tooth shells. Shell-fish have been used as food by man from prehistoric times. At various places along the sea-coast huge shell mounds or " kitchen - middens" are found as relics of the shell-fish devoured by past genera- tions, the antiquity of which is indicated by the primitive implements sometimes found in these mounds. The Oyster. — Of all molluscs, certainly of those found in America, the oyster, Ostrea mrginiana (virginica), is the most important eco- nomically. A generation or more ago there were dredged in Chesapeake Bay, one of the most famous regions for the production of this bivalve, each year, about 17,000,000 bushels of oysters. These oysters, which were the "wild crop" obtained without cultivation, were shipped alive and in cans all over the country. The supply was considered to be "inexhaustible." Other extensive beds are found in Long Island Sound, in Louisiana, at other places on both coasts, in Japan, and in various European countries. After this maximum dredging of the wild crop had continued for some years it began to be noticed that the supposedly inexhaustible supply was failing and, in 1882, Dr. W. K. Brooks, of Johns Hopkins University, was appointed by the Governor of Maryland, a commis- sioner to investigate the oyster business and to make recommendations for its improvement. The results of these and his previous investiga- 46 ECONOMIC ZOOLOGY h PIG. 29. — An oyster in the right valve of the shell, dissected so as to show the internal organs. The anterior end of the body is at the top of the figure, and the dorsal surface on the right hand. Xi. b, the mantle; c, the muscle; d, the heart; g, the gill; h, the lips; *', the intestine; j, the liver; m, the mouth; s, the stomach. (From Brooks, The Oyster.) MOLLUSCA 47 tions were published by Brooks in his book, "The Oyster," in which he described in a popular yet scientific way, the natural history of the American oyster, and showed the necessity of conserving the supply by proper cultivation just as is done with most other natural food prod- ucts. The food of the oyster consists of microscopic organisms living in the salt or brackish water in which the oyster thrives best. They are carried into the mantle chamber, Fig. 29, by the cilia cover- ing the organs of that region and enter the mouth of the animal. Among these organisms, of course, may be disease germs, if the water be polluted with sewage, as will be noted below. It requires three or four years, depending on the food supply, etc., for the oyster to reach maturity. In the European oyster the eggs are fertilized and begin their de- velopment in the gill tubes of the female, while in the American form it was found by Brooks that the eggs are fertilized outside of the female, in the surrounding water. Since an average Maryland oyster will lay the incredible number of 16,000,000 eggs per year, it is evident that the struggle for existence must be terrific or the sea would soon be filled with oysters. If the egg should happen to be fertilized, it segments and develops into a tiny ciliated larva which swims to the surface, where it may be killed by a heavy rain. After living for a time at the surface, if it escape its many perils, it sinks to the botUta, loses its cilia, devel- ops a tiny shell, and attaches itself to some solid object, if such be found, and is known as a "spat; " if no solid object be present the young oyster will perish, but if it succeed in becoming "set" it will proceed to develop into the mature oyster. Oyster Culture. — Brooks found that by mixing eggs and sperm from "ripe" oysters in salt water the eggs could be easily fertilized in un- limited numbers; but, for some reason, these artificially fertilized eggs when they develop to the spat stage will not set, so that this stage of oyster culture is not practicable. What may be done is to allow the spat to form in the natural way and then collect it by placing various kinds of hard objects in the water at the breeding season; if placed in the water too long before the spat are ready to set these solid objects, known collectively as "cultch," may become covered with mud or other sediment and thus prevent the spat from setting. Various sub- stances are used as cultch: tiles; a bunch of twigs (bamboo in Japan) tied together and sunk to the bottom with a stone; crushed rock; scrap 48 ECONOMIC ZOOLOGY tin from can factories; scallop shells; and especially oyster shells. New beds may be started by spreading the cultch over the bottom at the breeding season and then distributing "wild" oysters, that are about to spawn, over the cultch. After the spat has "set" over the cultch and has grown into "seed" oysters of an average size of half a dollar, the cultch may be collected, broken up and spread over the bottom again to prevent the growing oysters from crowding each other, Figs. 29 PIG. 30. — A bed of well-shaped, ^marketable oysters. Grave, from Brooks, The Oyster.) X Ko- (Photograph by and 30. This is the general method of oyster culture as carried on in many places. Of course, it necessitates a survey of all the oyster grounds, just as farms are laid out, in order that dishonest dredgers, of which there are many, may not reap where others have sown. It is also obviously more troublesome than harvesting the "wild" crop, but unless some sort of culture be adopted the wild crop will inevitably become exhausted. The most serious difficulty in such cases always MOLLUSCA 49 PIG. 31. — Upper figure, an oyster shell to which about 150 young oysters have attached themselves. Lower figure, a pipe from Chesapeake Bay upon which six oysters have grown. (From Brooks, The Oyster.') ECONOMIC ZOOLOGY is to get the proper legislation enacted by ignorant or dishonest legislatures. There are various difficulties with which the oyster farmer has to contend. If the water be too cold the oysters may grow but not repro- duce; if it be too shallow it may freeze in exceptionally cold weather; the salinity of the water may not be right. Although there are no known epidemic diseases of oysters, there are several enemies that cause trouble; the worst of these is the starfish, as has been noted in connection with the Echinodermata; while not found in the southern beds it is so numerous and destructive farther north as to make oyster culture impossible without active warfare against this enemy. They multiply very rapidly, where con- ditions are favorable. The best means of destroying them is to catch them on a " tangle," Fig. 32, of frayed rope and then kill them by plunging them into a tank of hot water. If cut to pieces and thrown back into the water the menace is increased, as many of the pieces will grow into com- plete starfish and thereby increase the total number of the pests. There are several snails, known as "drills" that are often quite destructive by boring through the shells, especially of young oysters. There are several fish such as the drum, sheepshead, skate, etc., that are injurious; and the oysters are sometimes smothered by mussels, sponges, sea-weeds and drifting sands. Oysters are collected with tongs or by dredging. The former, Fig. 33, might be compared to a pair of heavy iron rakes with very long handles that are joined, scissors- wise, near the rakes. The tonger may stand in the stern of a row-boat or at the side of a larger boat and by a scissors motion scrape off the oysters from the bottom until PIG. 32. — A "tangle" of frayed rope or cotton waste used to collect starfish from oyster beds. (After J. L. Kellogg, Shellfish Industries, from U. S. Fish Commission.) MOLLUSCA 51 his tongs are full and then lift them up and empty them in the boat. The size of the tongs varies, the shortest handles being about 12 feet. They are used by the poorer oyster men, often in water too shallow for larger dredging boats. While 10 to 15 feet is the usual depth, they may be used in water as much as 30 feet deep. Needless to say tonging is very hard and, in cold weather, very exposing work. The more modern and much more rapid method of collecting oysters is by means of the dredge, an iron frame with a heavy net behind to hold the oysters that the frame detaches from the bottom. The dredge FIG. 33. — Oyster tongs. Laboratory employees tonging and culling oysters in Louisiana. (After J . L. Kellogg, Shellfish Industries.) is used on larger sailing or steam vessels and may be hauled, by steam power, Fig. 34, from any depth at which the oysters are found. "Oys- ters that grow on trees" are a curiosity of the tropics, they are simply oysters that become attached to the submerged roots of aquatic trees (i.e., mangrove). The small mangrove oysters of the West Indies are collected and sold in considerable numbers. As noted above the oyster in feeding will take into itself any disease germs that may be in the surrounding water. The germs that enter the digestive tract are doubtless soon destroyed, but where present in 52 ECONOMIC ZOOLOGY the water they will adhere to the gills and other organs of the oyster and may, if the oyster be eaten raw, thus enter the human system. Although denied by some, there have been numerous cases of typhoid fever and other diseases that have been traced to contaminated oysters. It is claimed by some oystermen that during the cold weather, when oysters are most in demand, they are, in a sense, hibernating and take no food so that they cannot be seriously contaminated with disease germs. Whether or not, this be true it is obviously important to see that no oysters be sold that are taken from beds that are contaminated by FIG. 34. — A steam power oyster dredge. (After J. L. Kellogg, Shellfish Industries, from a Report of the N. Y. Forest, Fish and Game Commission.') sewage; most, if not all, of the States possessing oyster grounds now have laws that are supposed to prevent this danger. In some cases oysters from contaminated beds may be made safe by transplanting them for a certain length of time to pure water, until they are free from pathogenic organisms. There are federal laws that regulate the interstate shipment of oysters except in sanitary ways, either in the shell or in sealed tin or glass vessels, surrounded by ice. A bivalve that has opened its MOLLUSCA 53 shell is not fit for food but it cannot contaminate those that are still closed. The custom of " floating" oysters has been considerably discussed. By a "floated" oyster is meant one that has been brought into water of less salinity than that in which it grew, until it has absorbed this fresh water and thereby become swollen or bloated. This custom, when the fresh water is contaminated by sewage, as it often is near cities, FIG. 35. — Long-neck clam, My a, with byssus, b, attached to sand grains, sg. J. L. Kellogg, Shellfish Industries.) (After was a serious source of contamination and was justly condemned; but if the water be pure the floating merely makes the oysters bulkier (by as much as 20 per cent., at times), and thereby diminishes their food value, when bought by the quart or gallon. For this reason the pure food laws require "floated" oysters to be so labeled. The floating also diminishes the salty taste of the oysters, which makes them more agree- able to some palates. Soft or long neck dam, Mya arenaria, Fig. 35. This is the clam of New England, famous in clam chowders and clam bakes. It is 54 ECONOMIC ZOOLOGY essentially a northern form where it was formerly found in enormous numbers. It spends most of its time buried in the sand or mud, some- times to a depth of a foot. Its long siphons (neck) reach to the surface of the sand and are withdrawn when the sand is left bare by the re- treating tide, leaving the characteristic hole that reveals the presence of the hidden clam, Fig. 36. The clams are obtained by digging them a low tide with a sort of short-handled, long-tined rake, shown in Fig. 36. The number of clams obtained under favorable conditions from a given area is sometimes astonishing, Fig. 37. The shells being thin (soft), they are often broken in digging them out of the sand. FIG. 36. — Beach showing very numerous holes of long-neck clams. Clam rake in foreground. {After J. L. Kellogg, Shellfish Industries, from Report of Mass. Fish and Game Commission by Belding.) Clam Culture. — Although the conditions suitable for the culture of soft clams are quite different from those noted above for oysters, they are not unusual and are fairly well understood; it is estimated that 400 bushels per acre, at a profit of 75 cents per bushel, could be raised. The chief difficulty in the way of successful clam culture is that the laws of some States make the clam bottoms public lands, so that the man who cultivates clams has no legal right to protect his plantings against trespass and theft. This clam has been transplanted to the Pacific coast where it apparently thrives and may become an important source of food for that region. Hard or little neck clam, quahog, Venus mercenaria, Fig. 38. This clam is common along the entire Atlantic coast, but for some'rea- MOLLUSCA 55 son is seldom eaten in the south where it is most abundant. The massiveness of its valves has given the name "hard," the shortness of its siphons the name " little neck," and the name "quahog" or "quahang," is said to be derived from an Indian name meaning "tightly closed." The smaller specimens, which may bring $4 a bushel, are served in restaurants as "little necks," to be eaten raw from the half shell. Though sometimes found between tides, the FIG. 37. — Long-neck clams dug from beneath one square foot of a flat. Such a yield is unusual. The ruler is six inches long. (After J. L. Kellogg, Shellfish Industries, from Report of Mass. Game and Fish Commission by J. R. Stevenson.) quahog usually occurs in greater numbers in deeper water and is collected from such beds with a large rake with long, steel teeth and a han lie as much as 60 feet long, so that their collection is very laborious. The clam has few enemies in its natural habitat and is so very hardy that it may be transported almost any distance, even in warm weather. Like the oyster, many of the northern quahog beds were dredged 50 ECONOMIC ZOOLOGY till depleted, so that the canneries were compelled to move south to new beds. The only effort, apparently, to conserve the supply that has been made has been to declare an occasional closed season. Enough experi- mental work has been done to indicate that culture of this clam might be carried on at a good profit. Scallop, Pecten irradians and P. tenuico status, Fig. 39. These two species are found along the Atlantic coast, the former in more shallow waters, from Cape Cod to Texas, the latter in deeper waters, north of Cape Cod. The southern form seldom exceeds 3 inches in diameter and is the more common of the two, the. northern species may reach a diameter of 7 inches. PIG. 38. — Hard-shell clam or quahog, Venus mercenaria. X/^. PIG. 39. — Scallop shell, Pecten irradians. X- The only part that is usually eaten is the small, cylindrical adductor muscle, though the rest is perfectly good food. These meats are freshened by soaking them in fresh water; this process swells them greatly and of course increases the value of animals sold by bulk, though it makes them spoil much more quickly. Pecten does not lie buried as do the preceding two forms, but moves about more or less actively by opening and shutting its shell, so that it is dredged by means of a "pusher," a rectangular iron frame with a bag at the back. Owing to their perishability and the limited supply scallops are not used to any great extent at a distance from the coast. As the price is sometimes as high as $5 a gallon, wholesale, they may be consid- MOLLUSCA 57 ered a luxury. What might be expected from scallop culture it is difficult to say. Sea mussel, salt water mussel, Mytilus edulis, Fig. 40. The sea mussels have for ages been an important article of diet in Europe, but, for some reason, they have never become popular in America, though the natural beds would supply large quantities at a low cost, and by proper cultivation they might rival the oyster in importance ; Field (82) summarizes his investigations upon the sea mussels as follows: "i. The sea mussel, Mytilus edulis Linnaeus, is not utilized as a food to any extent in the United States outside of the vicinity of New York City. "2. As a food material it is superior to many articles which are com- monly eaten. Scores of persons have pronounced it to be equal in flavor, PIG. 40. — Edible salt water mussel, Mytilus edulis. X%. or even superior, to the oyster; it is easily digested, has a high nutritive value, and is exceedingly abundant and general in its range. "3. Along most of our eastern coast the mussel is in season for food when the oyster is out of season. "4. The mussel is well adapted to preservation. When canned or pickled it will retain its natural flavor for months. "5. The mussel breeds at a prolific rate, it develops rapidly, requires less special conditions for growth than the oyster, and may therefore be easily cultivated. ''6. The only difficulty in the marketing of mussels for food purposes is that they spoil quickly after being removed from the water. It is necessary to use them within 24 hours after they are collected or ptomaine poisoning may result. To insure one's self against illness from eating them, the mussels must be taken from water that is pure and subject to the constant circulation of tidal currents. 58 ECONOMIC ZOOLOGY "7. Other important ways for utilizing mussels are as bait for the fisheries and as fertilizer for the soil on which onions and carrots are to be raised ..." Edible Snails. — There are various species of snails that are used for food, most of them belonging to the common genus Helix; they are, of course, Gastropods. The eating of snails was known in Italy before the Christian era; the custom was introduced into France in the latter part of the eighteenth century which country is now the chief consumer of this mollusc. It is estimated that in Paris alone 200,000,000 snails are consumed in a season, September to April — the price varying from 50 cents to $2 depending on the species, quality, etc. They are a delicacy, not a staple article of food, like beef. Snail farms or "snaileries" are common in southern France, in Italy, and in Spain, though the business is not so profitable as formerly. The FIG. 41. — Shell of Abalone, Haliotissp. snails are collected in the woods by peasants; they are put in "pens" or "gardens" surrounded by a low fence of wire netting, about 10,000 snails in a pen 25-30 feet square. They are fed on all kinds of vege- tables or on bran-mash. Each snail lays about 50 to 60 eggs in the summer, which hatch and become sexually mature the next summer, but do not reach their full size until the second summer. They are cooked in various ways: i.e., they may be boiled, picked out of the shells, minced, flavored and then stuffed into the shells again. They could probably be easily raised in the United States in places that are useless for other purposes, but a popular taste would have to be created or they would have no market. Abalone, genus Haliotis, Fig. 41. This familiar gastropod of the western coast is useful both for food and in the manufacture of orna- MOLLUSCA 59 merits from its shell. In some species the shell when polished is wonderfully fine mother-of-pearl, with all sorts of brilliant colors. Window-glass shell, Placuna placenta, Fig. 42. This curious bivalve has shells so thin and flat that they may be cut into squares of 3 or 4 inches and set in window sash for lighting houses. Their pearly translucency is very pleasing, and they are very widely used in some parts of the tropics, for residences, churches and other buildings. "The demand for window shell in other countries for the manufacture of lantern shades, screens, etc., in addition to the local use for windows, has so increased that there is danger of exceeding the supply. In the early part of the year the Bureau of Science undertook the planting of a new bed of these shells. Five thousand live shells were taken in Kawit PIG. 42. — Window shell, Placuna sp., and square cut from a shell. xM- and planted on the mud bottom of the esteros and oyster beds at Malabon. I believe these will thrive, if they are not removed by the local fishermen." From repprt of Director Alvin Cox, Phila. Bu. Sc. Camto or helmet shells, genus Cassis. These Gastropod shells owe their value to the fact that they are composed of different colored layers — white and black for example — so that a figure may be carved out of one color with the other color as a background. The carving of cameos, so important in Italy, has, it is said, degenerated from an art to a trade, so that the fashion has greatly declined. Giant clams, genus Tridacna. These are the largest of the lamelli- branchs and may reach a weight of 500 pounds. They are found in the oriental tropics and are said to sometimes drown pearl divers who happen to be caught between their mammoth valves. The valves 6o ECONOMIC ZOOLOGY which may be a beautiful pure white color within are often used as fonts for holding holy-water in churches. In parts of Africa and India cowries or porcelain shells are used as money and the well-known wampum of the American Indians was made from the shells of the quahog, especially those that were lined with blue, and from the colored adductor muscle scars of other lamel- libranchs. FIG. 43 — A gastropod shell, Murex sp. xM- Pearls and Mother-of-pearl. — The shells of lamellibranchs are se- creted by the mantle. In most species this secretion is mainly a dull white calcium carbonate, but in some species it is laid down in glossy iridescent layers and is known as mother-of-pearl. If of a fine qual- ity, it may be used for various ornamental purposes; if of a less fine grade it may still be used in the manufacture of pearl buttons. The pearls, which may be attached to the inside of the shell or may be free between the shell and the mantle, are formed by the same glands of the MOLLUSCA 6 1 mantle around some small foreign body as a nucleus. This foreign body may be a grain of sand, a dead egg, a dead parasite, or a small shot or other object introduced by man between the shell and the mantle. The irritation of this foreign body probably causes an active secretion by the mantle glands of the nacreous material in concentric layers over the offending object, the result being a pearl, whose value depends upon its size, shape, color, etc. If the pearl be attached to the shell it will, of course, have to be cut free, which will leave a scar on one side and render it fit only for a setting where this side will be hidden. In some places, it is said, fine shot are introduced between the mantle and shell to act as nuclei for pearls; the oyster is then replaced in the water to be examined for pearls at a later date. This characteristic of the mantle has been made use of in producing the sacred clam shells that the Chinese Buddhists believe to have a mi- raculous origin, and that are sometimes seen in collections. Brooks (79) says: "The inside of the shell has a beautiful pearl lustre, and along it is a row of little fat images of Buddha, squatting with his. legs crossed under him, and his elbows on his knees. They are formed of pearl precisely like that which lines the rest of the shell, a little raised above its surface and outlined in faint relief, but they are a part of the shell, with no break or joint. In the process of manufacturing them, the shell of the living animal is wedged open, and thin images, punched out of a sheet of bell-metal, are inserted. The animal is then returned to the water, and is left there until enough new shell has been formed to cover them with a varnish of pearl thick enough to fasten them, and to hide the metal, while permitting the raised outline to be seen." Although pearls of considerable size are often found in the edible oysters and other bivalves they have little value, as the glands of the mantle do not secrete the proper nacreous material. The precious pearls are found chiefly in the pearl oysters of the family Amculidce and in the pearl-bearing mussels of the family Union- ida. The true pearl oysters are found in the Indian Ocean, Red Sea, Gulf of California and elsewhere, though the value of the pearls and mother-of-pearl varies greatly in different localities. In some places the*shells are heavy and of fine quality and may be worth 50 cents each; in other places they are thrown away and only the pearls are sought. 62 ECONOMIC ZOOLOGY The oldest pearl fisheries are on the north coast of the island of Ceylon, where pearls have been collected since the beginning of the Christian era. Since the British occupation the fisheries have been under govern ment control and have been a great source of revenue. At certain intervals the government will advertise an open season for pearl diving and the natives flock to the fishing grounds by the thousands. At a given signal, each day the boats set out, and at the end of the day a second signal recalls them to shore. Small boats are used, each with 10 divers, in two gangs, an equal number of helpers, and two or three sailors. The diver descends to the bottom, 30 to 50 feet, with the aid of a heavy stone, works for 30-90 seconds and is drawn up with his basket of oysters. At the end of the day the oys- ters are taken to shore and placed in bins to decay. When thoroughly decayed they are carefully washed and examined for pearls; the stench may be imagined. The government claims a certain proportion of the shells and the divers take the rest. It makes an interesting form of gamble, as a collection of shells may have $10,000 worth of pearls or it may contain none. For miles the shore is covered several feet deep with shells. In America the most important pearl fisheries are in the Gulf of California, centering about La Paz. These fisheries were operated by Indians in the time of Cortez and were exploited by the Spanish govern- ment. The season here is from June to December. The expert Indian and Mexican divers, who were said to work on an empty stomach to increase the lung capacity, have been largely replaced by the present operators, chiefly San Francisco firms. Each boat now has a diving outfit, with one diver and a proper number of pump men and other helpers. About 300 oysters per day are collected by such a boat. There are also 'fisheries on the coasts of Panama, Guatamala, Red Sea, South Sea Islands, Australia, the Sulu Islands, and elsewhere. In the latter two regions the shells are particularly fine and are collected for mother-of-pearl. At the town of Jolo, capital of the Sulu group the writer was asked one peso (50 cents) for a single valve of a large pearl oyster. Some of the fresh-water mussels (Unionidae), Fig. 28, of Asia, Europe and America are valuable both for pearls and for use in making pearl buttons. On account of their unusual color the pearls are often MOLLUSCA 63 very valuable, but in America they have never been very systemati- cally sought, being"mainly collected by farmers and others in a very wasteful manner. In Europe the supply has been conserved by care- fully opening the shells with specially devised tools and returning the animals to the water after examination. In America the Unionidae are chiefly used for buttons and along the Ohio and Mississippi Rivers they have been so extensively dredged that they are threatened with extermination. The shells are drilled with tube-shaped drills that cut out disks of pearl from about 5 mm. to 30 mm. or more in diameter, Fig. 44; from these rough disks the pearl but- FIG. 44. — Ohio River pearl mussel, Unio sp., from which 15 button discs have been cut. Above are 3 discs of different sizes. X/^. tons are made. Several dozen disks may be drilled from one shell, the number varying, of course, with the size of the disks and the size of the shell. In both the pearl-bearing oysters and pearl-bearing mussels pearls are most likely to be found in distorted and abnormal specimens. Ship-worms. — Of the few molluscs that are of negative economic importance probably the most injurious are the ship-worms, Teredo navalis and other species. In the days when all vessels were made of wood and were unprotected with metal sheathing these boring bivalves must have been, indeed, the ''terror of ships." Though they belong to the class of Lamellibranchs they are elongated, worm-like animals, and hence have been called ship-worms. They may reach a length of 64 ECONOMIC ZOOLOGY 4 feet and a diameter of i inch, Fig. 45. Sigerfoos (52) estimates that a single large female may lay 100,000,000 eggs. These eggs rapidly develop into free-swimming larvae, typical of the lamelli- branchs. After further development these larvae attach themselves FIG. 45. — A ship-worm, Teredo navalis, in a piece of timber. Xi. p, pallets; 55, siphons; T, tube; V, valves of shell. (From Hegner, College Zoology, after Cambridge Natural History from Mobius.) to some submerged piece of wood and begin to burrow into it, gradually changing to the worm-like form as they clo so. The newly attached larvae are tiny animals, abotft 0.2.$ mm., long; on entering the wood they grow rapidly so that in about five weeks, in some species, they FIG. 46. — Devil-fish, Octopus sp. may be 100 mm. long. Sigerfoos estimated that a four-foot specimen was only about a year old. The rate of growth seems to be independent of the kind of wood, whether it be soft white pine or hard oak; probably the food supply is the determining factor. In a four-foot worm the MOLLUSCA 65 valves are an inch or less in length and are the means by which the worm bores its way into the wood. The rest of the soft body is uncov- ered so that the animal secretes a thin, smooth calcareous lining to its FIG. 460. — Squid, Loligo pealii. burrow to protect itself from the rough edges of the wood. If the larvae settle at the end of a log they burrow straight ahead in the direction of the grain of the wood, but if they settle on the side of the log, they bore across the grain for a short distance, usually within 2 inches, 66 ECONOMIC ZOOLOGY then turn the direction of their operations so as to work with the grain, Fig. 45. As the worm increases in size it, of course, enlarges the di- ameter of its hole which thereby becomes conical in shape, as shown in Fig. 45. The much elongated body and siphons, Fig. 45, ss, extend posteriorly to the opening of the tube and the latter serve to conduct a FIG. 47. — A chiton. Xi. stream of water to the animal (just as in ordinary Lamellibranchs) from which food is extracted in the form of microscopic organisms. At the base of the siphons are two small calcareous bodies known as pallets, Fig. 45, p, which serve to close the opening of the burrow against an enemy or to retain the water should the low tide leave the wood exposed. The method of boring of ship-worms has been a much debated question; it is apparently accomplished by the rasping action of the posterior edges of the valves as they are rocked back and forth by the alternate action of the anterior and posterior adductor muscles, the shell being pressed against the end of the burrow FIG. 48.— by the cupping action of the foot. The particles of wood that are rasped away are ingested and thus Dentaiium. passed out of the burrow, but whether the animal de- rives any nourishment from them is a debated question. While the introduction of steel ships and the sheathing of wooden ones with metal have largely diminished the havoc wrought by these molluscan pests, still the destruction of small boats and especially of docks and piles, particularly in the tropical and subtropical waters, is often a serious matter. Various preventive methods have been tried, J MOLLUSC A 67 such as soaking the wood in creosote and other materials but they all seem to give only temporary relief. In the case of docks and wharves the difficulty is being overcome, in many places, by the use of concrete. The cephalopods, Figs. 46 and 460, are of comparatively little economic importance. The squid are used by fishermen for bait and are an important food for fishes. The rough white cuttle bone is used in bird cages, and the well-known pigment, sepia, is made from the ink of certain cephalopods, Sepia in particular. The Amphineura and the Scaphopods are of practically no economic importance other than as zoological specimens. CHAPTER IX ARTHROPODA This is a very large phylum of usually comparatively small animals; there are more species here represented than in all the other phyla combined. As their name indicates, they are characterized as the first animals yet studied that have regularly jointed appendages. They are like the annelids in being segmented, in having a mouth at one end and anus at the other; and in having a dorsal brain and a ventral, ganglionated nerve cord. They usually have striated muscle fibres, and are almost always lacking in cilia. -The body cavity is largely represented by blood sinuses in free communication with the vascular system. The classification is exten- sive but the most important classes are as follows: I. Crustacea, Figs. 49, 50, 51, 53, 54 and 55. These are arthropods in which four or five anterior segments are fused to form the head, while the rest of the segments may usually be divided into two regions, the thorax ist antenna; a2, 2d an- and the abdomen. Some of the thoracic segments may be fused with the head to form a cephalothorax, as in the crayfish. The head bears a pair of compound eyes, sometimes a median eye. The thoracic and abdominal appendages are variously modified as claws, legs, fins, ac- cessory reproductive organs, etc.; the typical appendage is biramous: the body is covered with a variously modified exoskeleton of chitin. Respiration is by means of gills or through the general body integument. 68 FIG. 49. — A water flea, Cyclops. Xio. tenna; e, eye; es, egg sac; od, ovi- duct; ov, ovary; t3, 3d somite; ui, uterus. ARTHROPODA 69 The circulatory organs consist of a contractile heart, a series of arteries and afferent sinuses and veins. The excretory organs are modified nephridia known as shell glands or green glands, located in and opening from the anterior part of the body. The nervous system consists of the brain, united by the circumoesophageal connectives with 'the ventral, ganglionated nerve cord. Sexes are separate or united; parthenogenesis is common. The class is divided into two subclasses, the Entomostraca and the Malacostraca. The former includes the smaller, simpler types, such as water fleas, barnacles, etc., Figs. 49, 50, and 51; the latter includes the larger, more highly organized forms such as crayfish, crabs, lobsters, etc., some of which may be several feet in extreme length, Figs. 53 and 54. FIG. 50. — Goose barnacle, Lepas sp. xM» II. Onychophora, Fig. 52. This class includes the curious cater- pillar, like genus, Peripatus, which is interesting as having character- istics of both the Arthropods and the Annelids — a sort of " connecting type." III. Myriapoda, Figs. 56, 57 and 58. These are the centipedes and millipedes. They have many of the characteristics of the insects. There is a distinct head, bearing jointed antennae; a pair of eyes and two or three pairs of jaws. The rest of the body is not marked off into different regions, but is divided into many segments, which in some species bear a single pair of appendages each (centipedes) and in other cases two pairs of appendages each (millipedes). They breathe by a system of trachea, like those of insects, opening to the exterior through stigmata on the lateral or ventral side of the body. IV. Insects. — These are the grasshoppers, bees, flies, beetles, butter- flies, dragon-flies, etc. It is the largest of all the groups of animals, 7O ECONOMIC ZOOLOGY both in number of species and, possibly, in the number of individuals, with the probable exception of the Protozoa. In some ways the insects are the most highly organized of the invertebrates, and exhibit an in- telligence far superior to that of many of the lower vertebrates. It is a very distinctive group, without the wide variations in struc- ture seen, for example, among the Crustacea; their name "Hexapod" FIG. 51. — Acorn barnacle, Balanus sp. Xi. indicates one of their most marked characteristics, the invariable pos- session of six legs, born on the thorax. There are usually two pairs of wings, also born on the thorax. The body is distinctly divided into three regions, head, thorax and abdomen. The respiratory organs are branching air-tubes, or trachea, extending all through the body. The FIG. 52. — Peripatus capensis, drawn from life. Somewhat enlarged. (From Hegner, College Zoology, after Sedgwick.) eggs usually hatch into a grub or caterpillar, and undergo a marked metamorphosis in development to the adult condition. The adult is terrestrial or aerial, less often aquatic, but the larval stages of many forms are strictly aquatic. Some forms, bees, ants, etc.; form complex communities, with marked polymorphism. V. Arachnida, Figs. 59 to 63. This rather heterogeneous class includes the spiders, scorpions, mites, ticks, king-crabs, etc.; though the ARTHROPOD A 71 classification of some of these is uncertain. There is usually a cephalo- thorax and an abdomen; in some cases these two regions are fused. There are no antennae in the adult. The cephalothorax bears sessile and usually simple eyes. The first pair of cephalo thoracic appendages are the chelicerae; the second pair are the pedipalpi; posterior to these are four pairs of legs. The respiratory organs are sometimes trachea, sometimes book-lungs, sometimes leaf-like external gills. The sexes are usually separate and there is no metamorphosis. Crustacea. — The American lobster, Homarus americanus. This is probably the most important of our Crustacea. As a laboratory form it is now rather expensive for large classes, but since the crayfish, Fig. 53, is almost an exact anatomical copy of Homarus, on a small scale, it is usually used for dissection purposes. The Atlantic Coast of North America is the greatest lobster ground in the world, though the lobster industry of western Europe is also important. The species under discussion is found from Labrador to North Carolina, but it is exceedingly rare toward the southern limit of its range; Maine and Massachusetts are the centre of the lobster industry. The Pilgrims found the Indians using the lobster for food and ever since that time it has been one of our most highly prized sea-foods. It is said the Pilgrims paid their debts in England from the products of their fisheries. Like so many of the natural resources of the country, all the natural lobster beds of the Atlantic are now more or less depleted and the price of lobsters has risen accordingly; a lobster that could be bought, a generation ago, for 5 cents will now bring a dollar or more. In Canada alone 100,000,000 lobsters have been caught in a year. The total catch in the United States in 1892 was about 23^ million pounds; in 1905 it was about nJ4 million pounds, which sold for more money than the catch of 1892. Some of the older accounts described monster lobsters that were "5 or 6 feet long," this probably meant with the claws extended straight in front of the head, which about doubles the length as now measured from the tip of rostrum to tip of tail. The largest authentic measurements that we have give a length, from rostrum to tail, of 23/x4 inches, and a weight of 34 pounds. As a medium-sized lobster weighs only five or six pounds, it will be seen that this 34-pound speci- men was a monster. The European lobster, Homarus gammarus, 72 ECONOMIC ZOOLOGY which is very similar to the American form, is said to be lighter in proportion to its length than the latter form. As to the age to which lobsters live we have but little data, Herrick (97) thinks one of the giant lobsters may be half a century old. A lo-inch female may be five years or more old. As in the crayfish the female lobster carries at certain seasons, a great mass of eggs with her, glued to the swimmerets on the ventral surface of the ab- domen by a secretion of the oviducts, such a female is known as a uberried" lobster and may carry 10,000 or more eggs. These eggs are carried until they hatch into tiny embryos that swim to the surface and look quite different from the adult lobster. After a long series of molts the growing lobsters gradually take on the adult form and sink to the bottom where they live. This process of molting is general among the Crustacea. Being inclosed in an inelastic chitinous exoskeleton the lobster can grow only by periodically shedding this exoskeleton and then expanding rapidly before the new exoskeleton hardens; the growth at one molt is sometimes surprisingly great. Molting among the adults is most common in the late summer and early fall. The process may take from 5 to 30 minutes or longer and it is generally five or six weeks before the new shell is thoroughly hardened. The Amer- ican lobster breeds biannually, though it is possible that annual broods may sometimes be produced. On land the lobster, owing to its weight and relatively weak legs is almost helpless, but in water it crawls about actively on the bottom and swims backward, by flopping its tail, at a remarkable rapid rate; one specimen was seen to swim 25 feet in less than one second. Varia- tions of temperature, food supply, etc., cause the lobster to migrate from shallower to deeper water and back, and even to travel along the coast for some miles. It may hide itself beneath rocks and such things or even dig a burrow in the mud, somewhat after the manner of the crayfish. It is carnivorous in habits and feeds most actively during the warmer seasons. In the early days the Indians caught lobsters by spearing them. In Europe they were caught by means of long wooden tongs. The method universally employed at present is by the use of traps or "pots, " built on the plan of the typical rat-trap, with a conical entrance at one or both ends. Traps of this sort have been used in Europe for centuries, being known in Scotland as "lobster creels." They were ARTHROPOD A 73 formerly of the wicker basket type, but are now usually made of lath. They may be rectangular, cylindrical or semicylindrical, and are from 2j^ to 4 feet long, about 2 feet wide and i J^ feet high. The ends are of heavy mesh in the form of an inverted cone with an entrance hole about 6 inches in diameter, so that the lobster can easily crawl in but cannot readily find its way out again. The slats are nailed about 2 inches apart on some sort of frame and have a door in the top through which the lobsters may be removed. The traps are baited with herring, halibut, fish-heads, etc.; they are sunk to the bottom with stones or other weights and are secured with a rope long enough to reach the surface of the water where it is attached to a wooden buoy, painted with the owner's name or color. The traps are usually set at a short distance from the shore, usually in i to 10 fathoms of water in summer, but in winter they may be out 5 or 6 miles, in 25 to 50 fathoms. The traps are pulled as often as once or twice a day in summer, but in stormy winter weather, a week or two may pass before they can be visited; many are lost in winter storms. After removal from the traps the lobsters may be kept in live boxes until ready for shipment, which is done by packing them in wet sea-weed, with ice below them in warm weather; the ice must be beneath as the dipping of the fresh water from the melting ice is fatal; the claws may be plugged or tied to prevent their being used. In this condition they may be shipped almost any reasonable distance. The longest distance they have been shipped was from England to New Zealand, about 12,000 miles; several such shipments have been made with comparatively little loss of life; each lobster in this case, however, was put into a separate wooden compartment with clear, cool, aerated water and was fed during the journey, which lasted, in one case, 54 days. Several lots of American lobsters have been transported across the continent and planted along the Pacific Coast from Monterey Bay to Puget Sound; while no definite results seem yet to have been attained it is probable that the experiment will eventually prove successful. When the supply of lobsters became seriously diminished means were sought to aid nature to replenish the waters that had been so thoughtlessly robbed. The most obvious thing to do was to strip the eggs from the berried lobsters and carry them through the earlier stages of their development 74 ECONOMIC ZOOLOGY in the safety of hatching jars. This is now done at numerous hatcheries along the coast, one of the largest of which is at Boothbay Harbor, Maine. The eggs after being carefully scraped from the swimmerets of the female are put into glass jars where they are kept in running water and carefully tended until they hatch and, preferably, have reached the bottom-seeking stage, when they are taken out to sea and liberated at favorable localities along the coast. Many millions of such young lobsters are liberated each season. Besides this rearing of young, other expedients are recommended and are being applied in some regions, as follows: 1. Have a standard trap with an entrance too small to admit the largest lobsters, which are thus saved for breeders, and with slats so far apart that lobsters less than 10 inches in length can escape. 2. License every lobster fisherman. 3. Protect the berried lobsters by forbidding their sale, and offer a bounty upon them at the hatcheries where they may be stripped. This bounty will tend to prevent dishonest fishermen from stripping the females and then selling them in the open markets. 4. Abolish the closed season and permit fishing throughout the year. Spiny lobsters, genus Palinurus. These lobsters which are often large and spiny but are without claws are found in various parts of the world. P. vulgaris, the common spiny or rock lobster is common in southern and western Europe and is an important article of food. It's meat is largely confined to the thorax and abdomen and is said to be as delicious as that of the true lobsters. P. interruptus is found on the western coast of North America and often reaches a considerable size. Crayfish, or Crawfish, genus Cambarus (eastern U. S.) and Astacus (Europe and Pacific coast of U. S.), Fig. 53. These two genera, of which there are many species, have a greater economic importance, both positive and negative, than is commonly realized. The positive side will first be briefly discussed. For many years they have been so extensively used as food in European countries that it has been profitable to rear them artificially. Their use in the U. S., though not so general, is increasing; for example, 16,000 pounds of Cambarus were sold from New Orleans Co., La., in a year, and over 55,000 pounds from Monroe Co., Fla. On the Pacific coast the larger genus, Astacus, is collected in large numbers, ARTHROPOD A 75 165,000 pounds being sold in Oregon in one year; these are prepared for shipment by placing them alive in white wine and spices, and boiling for two minutes; they are then shipped in this liquid in tin containers. The Astacus is not only larger but has larger claws and is more lobster-like than Cambarus, hence it brings better prices. It could doubtless be introduced into the east. The eggs are laid in the spring and the animal becomes sexually mature the following spring and reaches its full size in three or four years though these figures may vary considerably in different species and under different con- ditions. They can be easily raised in ponds, requiring merely air, fresh water and some sort of organic food; refuse animal and vegetable matter may be used. FIG. 53. — Crayfish, Cambarus sp. X^t- The damage done by crayfish, in certain sections, is very consider- able, especially in the clay lands of Alabama and Mississippi. The crayfish often dig holes into the ground to a depth of several feet, with the excavated earth piled in a circular chimney at the orifice. In these clay lands the bottoms of the holes are always filled with water, making ideal homes for the animals. In an area of about 1000 square miles the crayfish very largely prevent the successful raising of cotton and corn. They damage the young plants just after they appear, generally by tearing off the tender cotyledons. The number of crawfish in some of the infested areas may be seen from the fact that there may be 8000 to 12,000 holes to the acre, and on one plantation 27 barrels of crayfish were collected in a season, 76 ECONOMIC ZOOLOGY It is sometimes the custom to pay negroes a barrel of flour or of corn for each barrel of crayfish collected. The Department of Agriculture investigated the problem and found various remedies. Apparently if they are persistently hunted at twilight, at night, or after a rain, they may be exterminated or so reduced in numbers as to be of little harm. The easiest way is to pass along the rows and systemati- cally kill them with clubs or by stepping on them. If instead of this, they be collected, they may be either sold as food for man or they may be boiled, mixed with meal, and allowed to dry, when they make most excellent chicken feed. There are various poisons that when introduced into the holes and then filled in, will destroy the animals and leave them buried. Chlorid of lime, (one pound to three gallons of water) is effective and cheap, but the mixing and hauling may make it as expensive as carbon bisulphid, which may be introduced into the hole with a long oil can, such as locomotive engineers use, after which the hole is closed by stepping on it. The cost of the carbon bisulphid will be from $i to $2 per acre, or perhaps more in times of high prices, and the cost of the labor will perhaps be greater than the cost of the poison. Crabs. — There are many kinds of crabs that are used for food by man. In the tropics several forms of land crabs are thus used, some of them being collected in large numbers as they migrate from the mountains to the sea to spawn. In the United States it is the strictly aquatic forms, Callinectes and others, that are used, Fig. 54. These are used both as "hard- shell" and as "soft-shell" crabs; the former is the crab in its normal condition with the hard, chitinous exoskeleton; the latter is simply a crab that has recently molted, whose exoskeleton has not yet hardened. The hard-shell crab is caught either in traps, like those used for lobsters, or on lines baited with stale meat, the entrails of fowls, etc. No hook is used in "crabbing;" the crabber simply sup- plies himself with the necessary bait, with a dip-net and with a quantity of cheap twine. The twine is cut into suitable lengths and is tied to pieces of bait and the latter hung into the water from the side of the boat or dock, or at intervals along a long "trot line. " The fisher- man goes from string to string and pulls each up slowly until the bait is near the surface of the water, when, with a quick dip of the net, he captures the crab or crabs that may be clinging to the meat with ARTHROPODA 77 their claws. The crabs will drop off if the bait be raised out of the water. Sometimes two or three or even more crabs will be taken with one sweep of the net. With a dozen or less lines one person may keep continually at work and if the crabbing be good he will soon have more than he can carry home. The soft-shell crab does not allow itself to be thus easily captured, and hence is more of a luxury. Being unprotected with a hard shell it seeks safety by hiding itself under the sea-grass, etc., at the bottom, where it must be sought with a long handled net or by wading along the shore where the water is shallow. FIG. 54. — Common rock crab, Cancer irroratus. x%. The hard-shell crab is usually cooked by throwing it alive into boil- ing water, after which the meat, with the exception of certain parts, is picked out, seasoned and then baked, either in cakes or in the cleaned shells of the crab; such "deviled" crabs are very common in all parts of the country that are at all accessible to the coast. The soft-shell crabs do not have to be removed from their shells, but are eaten shell and all. Like some other sea-foods, crab meat, unless carefully prepared, quickly spoils and causes violent sickness. Like our other supposedly inexhaustible resources, the crabs have begun to become scarce, so that certain laws as to size, closed seasons, berried crabs, licenses for fishermen, etc., have been passed to protect this important industry before it is too late. 78 ECONOMIC ZOOLOGY Shrimps and Prawns, Fig. 55, are usually small Crustacea, of several species, found in various parts of the world. They are used in this country mainly for salads, and look like small, soft crayfish. In the tropics, the natives are often seen wading about in the shallow waters with a hand net that they sweep through the aquatic grasses, to collect these small (sometimes not over an inch long) Crustacea that are dried FIG. 55. — A shrimp, Palaemon sp. X%. in the sun and taken to market. In many parts of Europe they are ex- tensively used for food. In cans they may be transported any distance and will keep indefinitely, and it is in this condition that they are usually seen. Onychophora and Myriapoda.— These two classes are of so little economic importance that they may be dismissed with but a few words. FIG. 56. — Centipede, Scolopendra sp. X%. The former class probably has no economic importance other than its value for museum and scientific purposes. The centipedes, belonging to the latter class, are said to be eaten by the South American Indians. The myriapods are very generally feared though most of them are quite harmless. The large tropical cen- tipedes, genus Scolopendra, Fig. 56, are poisonous to man, possibly fatally so at times; they may reach a length of 18 inches. The well- ARTHROPOD A 79 known house centipede, Scutigera forceps. Fig. 57, is supposed by many to be very poisonous and, according to Marlatt, it has a decidedly disagreeable bite, which may be alleviated by the prompt application of ammonia; it feeds on roaches, flies and other insects, probably in- cluding bedbugs, so that it is a useful animal except for its poisonous bite. PiG. 57. — House centipede, Scutigera forceps. X/3- (From Marlatt, The House Centipede.) The millipedes, Julus and others, Fig. 58, are harmless to man but are often destructive to crops. Arachnida. — The economic importance of this group, which includes some animals of great zoological interest, is not great and is very largely negative. Spiders, Figs. 59 and 60. Some of the web-building spiders have a slight positive importance from the fact that the fine threads that they FIG. 58. — A milliped, Julus. X%. spin may be wound upon a reel and used for the cross-hairs of surveying and other instruments of precision. They are also of some value as destroyers of insects. Popularly the spiders are, as a group, supposed to be poisonous, even dangerously so. Students of spiders, however, have generally maintained that, with the exception of the huge, hairy tarantulas of warm climates, the North American spiders are harmless. Recently Kellogg (102) has pointed out that the notorious black widow 8o ECONOMIC ZOOLOGY spider, Latrodectus mactans, Fig. 60, really is at times, dangerously poisonous to man. Latrodectus is widely distributed over the earth and is generally feared. In the Americas there are three species of this genus, the best known being the one named above, which is found from the northern part of the United States to the southern end of South America, it is common in our southern and southwestern states. The male has an elliptical abdomen and is about 12 mm. in length. It is a "sooty-black or dark brown color with a conspicuous small blotch or blotches of vivid red on the under side of the abdomen. This blotch or pair of fusing blotches has the rough outline of an hour-glass. However it varies much in shape." The position and vivid color of this spot on the dark body are char- acteristic. Kellogg discribes a case in California in which most serious results followed the bite of this spider. Enormous swell- ing of the bitten organ, intense pains with cramp, labored respiration, slowed heart-beat, etc., were noted. A cat in- jected with an attenuated dose of the poison died in 10 minutes, other animals reacted strongly. FIG. 59. — "Tarantula" spider, sp. X^3- "A diadem spider of 1.4 gr. (weight), contains sufficient poison to destroy com- pletely all the corpuscles in 2.5 liters of rabbit's blood." Doubtless the effects of the bite of these spiders are more marked with some persons than with others and with the same person at dif- ferent times. Kobert says they may "produce by their bite the most serious general results, and are capable of killing even men." The bite of the Tarantula may often be painful without being serious. Of poisonous spiders Comstock (93) says: "The so-called Tar- antula (Heteropoda) that is frequently brought to the North in bunches of bananas is often described as the cause of serious injury. This however, though a large spider, is an inoffensive one. Mr. ARTHROPOD A 8l John T. Lloyd informs me that he has collected scores of specimens of this species with his hands in Samoa, where it is abundant, and has never been bitten by it. A c FIG. 60. — A, black widow spider, Latrodectus mactans, female. X3- B> ventral view of same; C, body of male. X3- (From Comstock, The Spider Book.) "Although we have in the North no spider that is to be feared, it is quite possible that in the South it is different. I confess that I should not like to be bitten by one of the larger Tarantulas of that region, although I know of no well-authenticated case of a person being bitten by one. 82 ECONOMIC ZOOLOGY "The spiders of the genus Latrodectus, of which we have a common representative in the South, are feared wherever they occur, and it is quite possible they are more venomous than other spiders." Scorpions, Fig. 61. These curious and dreaded animals with the "sting" at the end of the tail are often abundant in tropical and sub- tropical countries. The sting of a large zo-inch specimen may be seri- ous; that of an ordinary 3- or 4-inch animal is usually about as severe as the sting of a wasp or hornet. There are several small arachnids, of the order Acarina, that are external parasites on man and other animals and are sometimes a serious pest. For example, the tiny harvest- mites or chiggers burrow into the skin of man and cause most annoying itching; they may be killed by rubbing the skin with kerosene, a i per cent, solution of carbolic acid, or other similar substance. Poultry and cattle ticks, Fig. 62, cause in- jury to their hosts, the latter in particular as a carrier of the germ of the Texas cattle fever, as described in connection with the Protozoa. The follicle mites, Fig. 62, C, live in the hair follicles and sweat-ducts of man and cause "blackheads;" the itch-mite, Fig. 62, D, by burrowing in the skin produces intense itching, and the sheep-scab mite produces scabs on the skin of sheep, cattle and horses. King-crab or horse-shoe crab, Limulus, Fig. 63. This is perhaps the largest of living arachnids, reaching an extreme length of 2 feet. It is one of the few members of this class that live in the sea, where it is found crawling or slowly swmiming over the sand or mud flats along shore. It is interesting zoologically and is said to be fairly good as food, though it is not very commonly eaten. It is sometimes classed with the Crustacea, as its affinities are uncertain. Along the shores of Delaware Bay it is caught by the ton, as it comes ashore to spawn; it is used as food for hogs and as a fertilizer. FIG. 61. — Scorpion, Centrums sp. X%. ARTHROPOD A Insecta. — There are more species of insects known than of all the other groups of animals combined. Their numbers, though variously estimated, run well up in the hundreds of thousands, and the number of undescribed species can hardly be estimated. The study of this enormous class is a large department of science in itself, Entomology, and one of great importance largely because, as a class, insects are highly destructive to vegetation and injurious to man in other ways. It has been estimated that the direct annual loss in the United States due to insects is about one billion dollars, besides the losses due to dis- ease-producing and other noxious forms. D E PIG. 62. — Acarina, enlarged. C, follicle mite, Demodex folliculorum. D, itch mite, Sarcoptes scapici. E, sheep-scab mite, Psoroptes communis var. avis. (From Hegner, College Zoology, C and D, after Sedgwick, C, from Mengin, D, from Gudden, E, from Osborn.) The relation of insects to agriculture is too large a subject to even touch upon in a book like this; there are whole libraries of entomology dealing with this phase of economic zoology. It may be interesting, however, to briefly discuss a few insects that are harmful to man in other ways, and a few that are highly beneficial. Mosquitoes. — The part played by mosquitoes in the transmssion to man of malaria, yellow fever, etc., has already been noted in Chapter I. Though to most people all mosquitoes "look alike" there are sev- eral hundred species, and according to Felt (95) there are 50 or more species in New York State. Of these, two or three genera, have al- ready been mentioned; Culex, the common non-malarial forms; Ano- pheles, the malarial mosquito; and Stegomyia, the yellow-fever mosquito. The last named is ordinarily found only in tropical or sub-tropical 84 ECONOMIC ZOOLOGY regions, and is nearly always found in or about houses. It is sometimes called the "day mosquito" from its habit of biting in the daytime. This mosquito, Fig. 64, is black with conspicuous white markings; the legs and abdomen are banded with white, while the thorax is marked with white in the form of a lyre. Anopheles, the other important disease carrier may be distinguished from the non-malarial forms as follows: it has spotted wings, while most of the other forms have clear wings; it has long mouth palpi, shown ven- tral to the proboscis in Fig. 65; and when at rest the head and proboscis are in one line with the body and form a considerable angle with the surface, instead of being nearly parallel to it, Fig. 65; the position of the breathing larva, close to the surface of the water, is shown in the upper half of Fig. 66. TAs is well known it is the female mosquito that bites, possibly the male, in most cases, takes no food. The males may often be recognized by their large, feathery antennae, which have given them the name of " woolly heads." It is commonly supposed that they live upon blood, but it is likely that not one in a million ever tastes blood; their natu- ral food is generally the juices of soft plants, which accounts for the oenencial results of cutting down rank vegetation in the neighborhood of mosquito-infested houses. They may be kept in captivity by feeding them on ripe bananas. While there is some variation in the life-histories of the different species, the general process is about as follows: the female lays a number of eggs, either singly or in masses that float on the surface of the water; there may be several hundred eggs in one of these masses or "rafts," Fig. 67. The water may be fresh or salt, clean or foul; even cess-pools or wet mud may serve for some species. The water may be a lake, FIG. 63. — King or horse-shoe crab, Limulus Polyphemus. X%. ARTHROPOD A or it may be a few ounces in an upturned tomato can; it must, however, be still or the female cannot light upon its surface to deposit her eggs, hence rapid streams do not breed mosquitoes. The eggs hatch, depending on the species and upon the conditions, as soon as 16 hours after being laid, perhaps even sooner. The larvae, Fig. 66 and 67, FIG. 64. — Yellow-fever mosquito, Stegomyia calopus (faciata). Insects and Diseases, by Neivstead.) (After Doane, work out of the lower side of the eggs and begin their life as wrigglers, coming to the surface at frequent intervals to breathe through the air- tube near the end of the tail; this larval life may last from one to three or more weeks, during which time the insect molts several times until 86 ECONOMIC ZOOLOGY it finally reaches the pupa stage, Fig. 68, when it stops feeding and lies quietly on the surface of the water, breathing through tubes situ- ated on the dorsal side of the thorax, instead of near the end of the ab- domen. The larva is heavier than water and has to wiggle actively to get to the surface to breathe, the pupa is lighter than water and lies without effort at the surface. The pupal stage may last from two to six days or more. When the adult is ready to emerge the pupal skin splits down the back and the mosquito slowly escapes; it may take PIG. 65. — Resting position on vertical wall of Culex (left) and Anopheles (right). (From Howard, Mosquitoes of the United States, after the British Medical Journal.} Enlarged. several minutes for the animal to issue from the old skin and for its wings to dry and harden enough for flight; during this time it stands on the floating pupa skin and is, of course, easily upset and drowned by the least roughness of the surface of the water; this is another reason why mosquitoes do not breed in running water. How long the adult mosquito lives is difficult to determine; some of them hibernate all winter, but in confinement they usually die rather soon. Some species fly for considerable distances, but, as a rule, they re- main very close to their place of birth, so that it may even be possible ARTHROPOD A 87 to rid one suburban residence of the pest while the next place is still infested. They are delicate creatures and seldom attempt to fly in a strong breeze, but a very gentle breeze may carry them for a consider- PiG. 66. — Larva of Anopheles in feeding and breathing position, just below the surface of the water (upper figure). Larva of Culex in breathing position, at an angle to the surface (lower figure). Enlarged. (From Howard, Mosquitoes of the United States.) able distance. They are often carried for many miles in railway trains and other public conveyances to regions ordinarily free from them. Knowing their breeding habits, the methods of mosquito control will immediately suggest themselves; the first is to destroy all breeding places; this may mean the drainage of swamps and ponds or it may sim- 88 ECONOMIC ZOOLOGY ply mean the overturning of tin cans, tubs, etc. ; even a gutter on a roof that has become clogged with leaves and dirt may breed mosquitoes by the thousand. If the water cannot be led away nor poured out the problem may be handled in other ways; ponds that cannot be drained may be sprayed with kerosene or crude petroleum, about i ounce per 15 square feet once a month during the mosquito season; or if this be impracticable or undesirable, the pond may be stocked with minnows or other small fish that will feed upon the larval mosquitoes. These FIG. 67. — Culex pungens; egg mass, with more enlarged eggs at left; young larvee below. Enlarged. (From Howard, Mosquitoes of the United States.) small fish will be much more effective if the sloping banks of the pond be cut away so that the larvae may not escape the fish by going into the very shallow water close to shore. Dragon flies are excellent mosquito destroyers, as their larvae eat the larval mosquitoes and the adults catch and eat the adult mos- quitoes. Rain barrels, and cisterns can usually be screened to keep out the adult mosquitoes and this is one of the important proceedings in crusades against the yellow fever mosquitoes in the South. In some of the great swamps of the South, the extermination^ .qf mosquitoes is a difficult, if not impossible, task; but in most localities ARTHROPOD A 89 a pest of mosquitoes is a reflection upon the ownership or upon the local government. The house-fly, Musca domestica, Fig. 69. An even more serious pest than the mosquitoes are the flies, the house-fly, in particular. This only too familiar animal has, until recent years, been regarded as rather PIG. 68. — Culex pungens; full-grown larva at left; pupa at right. (From Howard, Mosquitoes of the United States.) Enlarged. an innocent little nuisance that tickled us when we wanted to sleep, and got into our food. That this idea is still somewhat prevalent is seen in the attitude of the average person toward flies and roaches; if the comparatively harmless roach finds its way into our soup we throw ECONOMIC ZOOLOGY it away in disgust, but many a housekeeper will fish half a dozen filthy flies out of the milk pitcher and "shoo" them off the cake without a thought. To most persons " all flies look alike " and they do not realize the number of species that are a pest to man and to the lower animals. FIG. 69. — The house-fly, Musca domestica. (After Doane, Insects and Disease.) For example, the sheep bot-flies lay their eggs in the nostrils of sheep and when the larvae hatch they crawl up into the frontal sinus causing great suffering to the sheep and loss to the owner. The horse bot-flies lay their eggs on the body of the horse and when ARTHROPODA the horse licks himself the eggs get into his alimentary canal where they hatch into maggot-like larvae. The bot-fly larvae of cattle, the ox warbles, get into the alimentary canal in the same way, but instead of lodging in the stomach they bur- FIG. 70. — Wing of stable-fly, Stomoxys calcitrans. Disease.) (After Doane, Insects and row out through the esophagus until they come to lie under the skin of the back; here they develop and make ugly sores, and when mature they cut through the skin, fall to the ground and complete their develop- PIG. 71. — Wing of house-fly, showing adhering dirt in which bacteria may lodge. (After Doane, Insects and Disease.) ment. The holes they make in escaping injure or even ruin the skin for leather. The human bot or screw-worm flies lay their eggs in sores on the body; the eggs very quickly hatch and the maggots burrow under the skin causing painful and even fatal results. 92 ECONOMIC ZOOLOGY The widely prevalent and dangerous disease of horses and cattle in the orient, surra, is probably conveyed by flies, as was noted before. Numerous other illustrations of the injury wrought by various species of flies might be given. Anyone will recognize the difference between the house-fly and the blue bottle fly or the horse-fly or, perhaps, even between it and the simi- lar stable-fly. Fig. 69 is an excellent representation of the house-fly, and a comparison of Figs. 70 and 71 will show- one of the means of dis- tinguishing it from the similar stable-fly; it will be noticed that the lowest or most posterior of the three long veins in the wing of the house- fly bends upward or cephalad at almost a right angle while the corre- FIG. 72. — Last three segments of the leg of the house-fly, showing claws, pulvillse and hairs. (After Doane, Insects and Disease.) sponding vein in the stable-fly's wing has only a wide curve toward its distal end. What is the reason for the present crusade against the house-fly? It is not merely because it is such a filthy little animal, as will be pres- ently noted, but because it is one of the worst carriers of pathogenic bacteria that we have; this is particularly true of the germ of typhoid fever, but it is thought that several other diseases are spread in the same way, such as tuberculosis, cholera, dysentery, smallpox, diph- theria, etc. It has been suggested that we call the house-fly the typhoid fly to remind people of its dangerous habits. The fly is an ideal in- strument for carrying bacteria, which it does in two ways; it may eat them with its food and then deposit them on our food or dishes in its excrement as "fly specks," or it may carry them mechanically entan- ARTHROPOD A 93 gled in the hairs and folds of its proboscis, wings or legs. The wings of. a fly when examined under moderate powers of the microscope are found to be covered with thousands of tiny, stiff hairs, too small to show in the figures here represented, and the legs are covered with numerous larger hairs as shown in Fig. 72. In the dirt (see Fig. 71) that collects among these hairs is room for millions of bacteria, so that in a series of FIG. 73. — Eggs of the house-fly. X i . (From Howard, House Flies, after Newstead.) experiments it was found that on an average a single fly may carry about 1,250,000 bacteria; these bacteria may be harmless but they are often the germs of deadly diseases. Let such a fly crawl across a culture dish and an astonishing trail of bacteria will develop along its course. Where these bacteria are collected is easily understood when the breeding 94 ECONOMIC ZOOLOGY habits of the house-fly are studied. Nearly anyone knows that the unpleasant maggots seen in decaying flesh are the larvae of flies, hatched from the eggs laid in this flesh by the adult females in order that these larvae may have food to eat while they are developing into the pupa or chrysalis stage. These maggots may or may not be the larvae of house- flies, probably they are mostly those of other species; but anyone may see the whole process by watching a piece of stale meat some summer's day. Usually one will not have to wait very long until a fly will light upon the meat and will proceed to deposit her elongated, white eggs, possibly at the rate of four or five per minute until a hundred or more have been laid, Fig. 73. If the meat be kept moist and warm the next day will probably see it swarming with tiny white maggots; these larvae, in a few days, will grow to full size, will surround themselves with little cases and become pupae. If the meat be in a covered vessel the flies that emerge in a week or more, from these chrysalises, will be caught and they will in turn, lay a new lot of eggs, though it may be a couple of weeks after hatching before the flies become sexually mature and are able to lay eggs. Since each fly may lay one hundred or more eggs in each of five or six lots per year, and since the whole life cycle, from adult to the next generation of adults, may take place in three or four weeks, it will be seen that by the end of the summer the descendents of the first few flies are to be numbered by millions; hence the importance of " swat- ting" the first flies as they emerge from their hibernation quarters. The life history of the house-fly is about as outlined above, except that its favorite breeding place seems to be in damp horse-manure, though it will breed in almost any kind of filth or decaying organic matter; for this reason the name " filth" fly has been suggested. It is perfectly obvious that if the eggs be laid, as they often are, in human excrement from a person who is suffering or has recently suffered from typhoid fever the flies, as they hatch and crawl out through the filth, may be cov- ered with typhoid fever germs which may be carried to another person in various ways. The disgraceful epidemics of typhoid fever that raged in our army camps during the Spanish American war were probably largely due to the lack of care in protecting the soldiers against this kind of infection. In a similar way flies, by feeding on the sputum (as they often do) of tuberculous persons, may carry the germs to other persons. Knowing, now, the habits of the house-fly the methods of fighting this serious pest are more or less obvious; they consist chiefly ARTHROPOD A 95 in destroying its breeding places, and secondarily in the use of fly-traps, fly-paper, etc. In towns and cities this is comparatively easy; on the farm it is far more difficult. The screening of privies and cesspools, and the close covering of garbage cans is generally not difficult. It is the handling of manure, particularly horse manure, that is difficult. In cities it is comparatively easy to compel owners of private and livery stables to keep all manure in closely covered bins so that flies cannot gain access to it; but on the farm this is far more PIG. 74. — Maggot trap for control of house-flies, showing the concrete basin of water in which the larvae are drowned, and wooden platform on which the manure is piled. (From Howard, House-Flies, after Hutchinson.) difficult. If not practicable to keep it in bins the manure should either be spread on the fields every day or two where it will dry and kill the fly eggs and larvae, or it must be sprinkled with some substance that will kill the flies without injuring the manure; various chemicals have been tried for this purpose with the conclusion that powdered hellebore (using 3/2 lb. to 10 gallons of water for each 8 bushels of manure) is the best substance, though its cost, about 0.69 cents per bushel of manure, makes it fairly expensive. Perhaps the best, and in the end the cheap- est, solution of the problem is to build a " maggot trap" to hold the ECONOMIC 20OLOGY manure; this consists of a wooden platform of slats over a shallow concrete tank of water. The manure is piled on this platform and is kept wet; the maggots in their migrations fall through the slats and drown in the water. This very simple arrangement, Fig. 74, is said to destroy 99 per cent, of the fly larvae in the manure. Details of construction and operation may be obtained from the U. S. Depart- ment of Agriculture. The trapping and poisoning of the adult fly is understood by most persons and a vigorous campaign along this line undoubtedly helps A R FIG. 75. — Termites. A, male or king of Termes slightly enlarged; B, female or queen of Termes, slightly enlarged. C, worker and D, soldier of Termes, consider- ably enlarged. (From Hegner, College Zoology, after Cambridge Natural History, C and D from Grassi.) diminish the numbers of flies, though not so effectively as the methods just mentioned. This subject is also treated in the bulletins issued by the Department of Agriculture. Termites or "white ants," Fig. 75. — These interesting insects are not true ants; they are variously classified by different writers, but are usually placed in the order Neuroptera. There are a hundred or more described species and many species that have never been named. Their colonial mode of life and their superficial resemblance to ants have doubtless given them the name "white ants." As among the hymenopterous colonies, the termites exhibit several forms of indi- ARTHROPOD A 97 FIG. 76. — Work of western white ant, Calotermes sp., in Mexican walnut, Catalina Mountains, Arizona. (From Snyder, White Ants as Pests in the United States and Methodsjof Preventing their Damage.} 98 ECONOMIC ZOOLOGY viduals, Fig. 75, the workers, soldiers, kings and queens; of these the workers are the most numerous and are the ones that do the damage. In some tropical forms the queen is many times as large as the other forms. In warm places eggs may be laid at any time during the year. At times, usually spring or fall, certain winged sexual individuals leave the nest in large numbers and swarm in new places to start new colonies. These " flying" ants are often destroyed in enormous numbers by birds. Termites are natural wood destroyers and live in colonies of usually several thousand individuals in decaying logs, dead trees, foundation PIG. 77. — Book from a library at Van Buren, Ark., ruined by white ants. (From Snyder, White Ants as Pests in the United States and Methods of Preventing their Damage.) timbers of houses, fences and other wood in contact with the ground, and in complicated underground passages usually found beneath wood or other debris. They sometimes work from these colonies up into the lower floors of houses where they riddle the floors and joists with their passages until nothing but a shell is left and their presence is first made known by the sudden collapse of some timber. It is in this destruc- tion of woodwork that the white ants do their greatest damage, es- pecially to timber that is in contact with moist ground, and particularly in tropical and sub-tropical regions, the ravages have been reported as ARTHROPODA g§ far north as New Hampshire and Michigan. In the tropics the damage is so serious that in some places all important buildings are being constructed entirely of concrete. In hard wood their main passages usually follow the course of the grain, as shown in Fig. 76. Besides the damage done to wood, just noted, many other products are injured; for example: books, Fig. 77; clothing, food, etc., espe- cially if stored in damp, dark, poorly ventilated cellars; shrubs, flowers and nursery stock; and field crops of various kinds. As in most cases, "an ounce of prevention is worth a pound of cure," and it is better to protect property against inroads of white ants than to drive them out after they have come. T. E. Snyder, (106) of the U. S. Department of Agriculture gives the following sum- marized recommendations, both for the "prevention" and for the "cure:" "How Buildings Should be Constructed so as to be 'White Ant Proof.' "Where possible, make the foundation of buildings entirely of stone, brick, or concrete, including stone columns or pillars in the basement to sup- port the floor above; make the walls and flooring in the basement or cellar also of concrete, and lay concrete floors on a giavel base. Fill in and round off points of juncture between concrete walls and flooring so that these will not meet at right angles. "Where stone or concrete foundations are impracticable, use timber im- pregnated with coal-tar cieosote. "Never completely surround beams with mortar or brick; leave an air space around the beams to permit air circulation. Set beams on stone or on concrete, not in the earth or in moist concrete. Rest the supports of porches or steps on stone or concrete. "Lay basement window sills and frames over concrete and do not allow the woodwork to come in contact with the ground. Never sink untreated timber in the ground or in moist concrete; let there be no wood in contact with the ground through which the termites may come up from subterranean galleries. "Complete dryness of the foundation and basement walls and flooring is an important means of rendering buildings safe from attack; therefore, provide for air spaces between the ground and wooden flooring and lay concrete floors on a gravel base. "In greenhouses, replace woodwork, wherever possible, with iron frames and concrete work. Treat necessary woodwork, before use, with a i per- cent, solution of bichlorid of mercury. "How to Eliminate White Ants Already Established in Buildings. 100 ECONOMIC ZOOLOGY " Promptly examine the foundation timbers and other woodwork in the basement to determine the approximate point of entrance and the extent of damage already accomplished. After removing the damaged wood, drench the ground with kerosene oil. "Break up the earthlike shelter tubes by means of which white ants are sometimes able to pass over the surface of impenetrable substances in order to reach woodwork, and drench the ground beneath with kerosene oil. "Then replace damaged timber with rock, brick, or concrete; or, if this be impracticable, substitute, for the foundation, timbers treated with coal- tar creosote. "Since termites always require access to damp earth, shut off this source of moisture, and the insects will not be able to extend the galleries farther and will perish." Clothes Moths. — It is probable that these small moths have been a pest ever since man began clothing himself in skins and they are particularly mentioned in the older books of the Bible. They are supposed to be of Old World origin and to have been introduced into America in early Colonial days. They are common everywhere; in the warmer regions being destructive at all times while further north they begin their depredations with the advent of spring or early summer. The adults, like other lepidoptera, are quite harmless as they take no food in the winged state, the mouth-parts being rudimentary. Though the average housekeeper does not know this, it is perfectly proper to kill the tiny flitting moths since it prevents their laying eggs that will hatch into tiny larvae or caterpillars, which are the destructive agents. The way in which these small caterpillars injure woolen goods, furs, etc., is only too familiar, so that nothing need be said of this. The adults lay their eggs usually upon clothes or other fabrics that are not in daily use, especially if these materials are in dark places; and if not disturbed these eggs soon hatch into the larvae that ruin the garments upon which they feed and from which they construct their tiny bag-like cocoons. Fig. 78 is the common species in the north; there are also the southern clothes moth, the common species from Maryland, south; and the tapestry moth, the rarest of the three, a more brightly colored form that feeds especially upon carpets, upholstering, and other heavy fabrics. The most important^ thing to know about all of these species is how to prevent their damage; this^is a very simple matter if we remember that the adults cannot and the larvae will not, eat paper . ARTHROPOD A; '.;•".', ^ 101 Every housekeeper knows that cloths, , and ; other ; ;wojol$ijL goods that are in daily use are seldom if ever dairiaged and that frequent vigorous shaking and brushing of clothes not in use prevents their being eaten by moths; this means simply that the eggs, if they have been deposited on the clothes by the winged adults, are brushed off and destroyed before they have time to hatch into the feeding caterpillars. The common method of putting away winter clothes in boxes or closets with moth-balls or other strong-smelling substances will be effective only if all eggs or larvae have been removed from the clothes by vigorous brushing and shaking before putting into the box FIG. 78. — The case-making clothes moth, Tinea pellionella; adult, larva, and larva in case. (From Marlatt, The True Clothes Moth, after Riley.) The strong odor will probably keep the adults from coming through the cracks into the box to lay their eggs, but if the eggs are already there, they will probably hatch into the destructive larvae which will not be affected by the smell. As the smell of naphthalene and other repellants is of ten disagreeably persistent in clothes that have been so protected, it is well to know that it is entirely unnecessary to use these substances if the clothes be tightly wrapped in stout paper, after being thoroughly brushed. For years the writer has, each spring, packed his winter clothes in the pasteboard boxes used by tailors, and then tightly wrapped each box in several thicknesses of newspapers, creasing all corners to prevent the possible entry of the slender little moths. In no single case has any damage been found on opening these boxes in the fall. The 102 ECONOMIC ZOOLOGY same results may' be secured by gumming strips of paper over the joints of the boxes. Upholstering of furniture, etc., that cannot be protected in this way while not in use during the summer may be protected by spraying with naphtha or benzine, every six or eight weeks, if precautions against danger from fire be taken with these inflammable liquids. In some of the regular storage warehouses, where such goods may be sent, cold storage is now used to protect goods against moths; sometimes in such warehouses periodic fumigation with sulphur dioxide or other gases is also practised, which has the additional effect of killing all rodent and other pests that may be present. In modern houses with well-fitted fly-screens clothes moths are, of course, to a large extent, excluded. Other Household Pests. — Roaches usually accompany filth, though they sometimes are found in cracks under wash boards, in cupboards and in other places where food stuffs are kept. They may usually be exterminated by a vigorous cleaning of cracks and corners and the use of borax or some regular roach powder that is sprinkled about in the places where they are seen; powdered sodium fluoride is said to be effective if used in this way. Bedbugs, the horror of the good housekeeper, are sometimes a pest in the most carefully kept house in the city, since they apparently come through cracks in the walls from adjoining houses which may not be so carefully looked after. The use of modern iron bedsteads elimi- nates largely the harboring places for this disgusting pest, and in old fashioned wooden beds they may be killed by spraying the cracks with benzine, or similar fluids, care being taken to avoid all lights while using these liquids. In cases of bad infestations with these or other household insects, fumigation with hydrocyanic acid gas is most effect- ive, but owing to the extreme deadliness of this gas it should only be used according to rigid directions such as are furnished by the U. S. Department of Agriculture. Fleas occasionally, for some reason, multiply very rapidly and in- fest dwellings beyond the point of endurance. In single rooms they may sometimes be exterminated by. filling the air and covering the floors with pyrethrum insect powder and closing the rooms for some hours; the powder may then be swept up and burnt. In cellars and ARTHROPODA 103 places filled with goods, fumigation with hydrocyanic acid or sulphur dioxide may be used. Red ants sometimes become so extremely numerous as to be exceed- ingly annoying. In tropical countries these tiny insects are often so numerous that it is necessary to set each leg of the dining room and kitchen' tables in a cup or small pan of oil or water to keep the food from being covered with them. In going from Hong Kong to Canton, China, by the night boat, a few years ago, the writer without thinking, put a package of sandwiches on the shelf in a small closet in his state- room. Early the next morning, six or seven hours later, when he went to get his sandwiches they were an almost solid mass of tiny red ants and had to be thrown overboard. In houses the red ants may be fought in the same way as the roaches and fleas, but, owing to their small size and large numbers, their extermination is often a matter of considerable difficulty. While a large majority of the insects are injurious to man, as has been said, there are numerous forms that are of direct or indirect benefit to him. For example : there are numerous insects that are used as food by the natives of the tropics. The best known of these are the grasshoppers or locusts. "Locusts and wild honey" are mentioned in the Bible as food. In the markets, of Manila, for example, may be seen on the stalls piles of grasshoppers with the appendages removed, ready for cooking. They are cooked in various ways or may even be eaten raw; though the raw locusts are said to be of very disagreeable taste. The cooked ones are said to be really delicious. Nearly every sort of insect is used as food by various savage tribes in various parts of the world, especially the fat, juicy grubs or larvae of beetles, and lepi- doptera. The enormous queen termites, noted above, are also eaten. Honey-bees. — A more universally esteemed insect diet, especially among civilized peoples, is honey, which has been an article of food from earliest times, the Bible speaking^of various lands that "flowed with milk and honey." It was probably the "wild" honey that was first used, just as it is still used occasionally, when a "bee-tree" is discovered; but the keeping of bees in hives so that all the honey made by them might be easily gathered is an ancient custom, probably origi- nating in Southern Asia, or in the East Mediterranean region. The United States is now the greatest producer of honey; in 1900 there were produced 61,000,000 pounds of honey, besides 750,000 pounds of bees- 104 ECONOMIC ZOOLOGY wax. Many large apiaries are to be seen in California, often on a sunny slope on the edge of a desert. In this state there is a succession of flowers throughout the entire year whereas in colder climates there is a winter season during which no honey is manufactured. The various flowers visited by the honey bees, of which bees there are some 1500 species, often give a characteristic taste to the honey, as happens for example, in some sections, when buckwheat is in bloom and the bees swarm over the fields of white blossoms. It is said that honey is some- times made poisonous by the bees visiting the flowers of Mountain Laurel. Honey is not only a delicious food, but is a highly nutritive one; it is also used in medicine. It is frequently adulterated with as much as 75 per cent, glucose, which process, though it is a true adulteration, does not injure the honey as food. Silk-worms. — The manufacture of silk originated probably in China about 3400 B. C. and is hence one of the oldest of human industries. The raising of silk- worms was introduced into Europe in 552 A. D. and into Virginia about 1600. The production of raw silk has never been profitable in America because of the competition with cheap Italian and Oriental labor for picking the cocoons and reeling the silk. The introduction of power looms, such as may be seen at Paterson, N. J., a great silk centre, has revolutionized the manufacture of silk goods, but in Canton, China, and doubtless in other places in the Orient, the old-fashioned hand loom, crude and terribly slow, may still be seen. China and Japan are great producers of raw silk and can probably increase their supply almost indefinitely to keep up with the demand. Japan exports some 11,000,000 pounds per year, 60 per cent, of which comes to the United States. The original source of the raw silk is, of course, the "silk-worm," the larvae of a moth, of which there are 15 to 20 species; the best known of these silk-worms is Bombyx mori, whose habits are, briefly, as follows: The female lays from 200 to 500 eggs, which hatch, the following spring, into tiny caterpillars; these larvae grow very rapidly, feeding voraciously on mulberry leaves, until they are about 3 inches long, molting several times; each larva then spins a cocoon of silk threads from 2000 to 3000 feet long, taking about five days for the process. The spinneretts are in the mouth and the silk-secreting glands (like ARTHROPODA 105 the web-secreting glands of spiders) extend nearly the entire length of the body. The animal swings its head from side to side, hour after hour, carrying a tiny thread of silk across with each vibration of the head. From this cocoon the adult moth hatches in 15 to 20 days, lays her eggs and dies. The cocoons that are used for silk are heated to kill the inclosed larvae, for if allowed to hatch they would cut FIG. 79. — Caterpillar with cocoons of the pupse of ichneumon fly parasites and (above) one of the adult ichneumon flies. The lines indicate natural dimensions. (From Jordan and Kellogg, Animal Life.) the silk threads in emerging. Sufficient numbers of cocoons are kept alive and allowed to hatch for breeding purposes. The utmost clean- liness and proper temperatures are necessary for the best results. The white mulberry furnishes the best food for the larvae, though the black mulberry, osage orange and other trees may be used. 106 ECONOMIC ZOOLOGY Probably all the conditions for the production of raw silk could be as well met in this country as anywhere else except that of handling the cocoons; so long, as this must be done by hand, it is not likely that the industry here can successfully compete with the cheap Oriental labor, as noted above. Among the beneficial insects, perhaps the most important are those that help us control the destructive ones. These may be divided into the predacious forms that attack and devour other insects, and the parasitic forms that spend a part of or all their lives on or in the bodies of other insects. Among the predacious forms the ladybird- beetles are perhaps the most important. These little beetles destroy enormous numbers of scale-insects, plant-lice, etc. One of the best examples of their work is seen in the work of the Australian ladybird- beetle, Nowus cardinalis, that was introduced, some years ago, into California to control the cottony-cushion scale that threatened to de- stroy the citrus fruit industry in that State. The beetles soon had the scale under control and it is now no longer considered a serious pest. Other species of ladybird-beetles have been successfully introduced into the United States and many of our native species are destructive to certain species of aphis and scale-insects. Among the parasitic insects are many that like the ichneumon flies, lay their eggs upon or in the bodies of caterpillars; when the eggs hatch the larvae feed upon and eventually kill the caterpillar, but not until the parasites have reached the pupa stage, ready to trans- form into the adult insects which repeat the process, Fig. 79. But for the work of these predacious and parasitic insects the control of the destructive forms would be a much more serious problem than it already is. The value of dragon flies in the destruction of mosquitoes has alreadv been mentioned. CHAPTER X PISCES The animals discussed in this and the following chapters all belong to the phylum Chordata. This rather diverse group contains animals that, at first glance, seem to be very slightly related; but it will be found that they all possess, in a more or less typical condition, at some period in their life-history, three structures or groups of structures that are characteristic of the phylum. The first of these is the notochord, a longitudinal, dorsally placed, cylindrical, skeletal axis, Fig. 80, nc, which, in the lower members of the groups, persists throughout life, while in the higher forms it is replaced, in the adult, by a cartilaginous or osseous back-bone. The second chordate character is the possession, either in the em- bryonic state or throughout life, of a series of slit-like openings between the pharynx and the exterior; these are the gill or visceral clefts, Fig. 80, g. On the visceral bars, the tissue between the clefts, are found in some forms, particularly the fishs, numerous branching, vascular structures, the gills, by which the animal extracts oxygen from the surrounding water. The third chordate character is a dorsally placed, hollow, nervcus system, Fig. 80, s.c. The phylum chordata is usually divided into three or four sub-phyla somewhat as follows: i. Enteropneusta, a few worm-like animals of rather doubtful relationships. 2. Tunicata, sea-squirts and other jelly-like animals that are more or less common in the sea. 3. Cephalo- chorda, a small group of small, fishlike animals, called lancets, Fig. 80, which exhibit in a very typical way the above-mentioned three chordate characters and are hence extensively used to illustrate a typical chor- date. 4. Vertebrata, a large and important group, including all of our common domestic animals and others having a vertebral column or back-bone. Of these four subphyla only the last has any appreciable economic value except as zoological specimens or objects for study, so that the first three need not be considered further. 107 ECONOMIC ZOOLOGY *l $s a o ±j 3 >* iifii «!l £**< : |a|3Ji g«^-g« ^.s^ss **ja>s I § i a 1 fc4 ° O 0> «£ W ^ «- ^° s s « "4T35S x Sis o> e ^"•"l! O -H bo « o ni rrt ^H -*A ZL '•£ S « "5 g S5^ v-g^ 1^2 T3 ••83 s|-i §to e ° J2 r^H dj ^-^ bo ^ °*^ § ^ ll ^'o « ^ ftocfi a I *a • ^^ e § "O v^l ° •a bo 14 :i ^1 •s". •§•& s C r^ ff.9 t s. The subphylum vertebrata, the most important of all the animal groups, is variously divided, by different authors, into classes. The older classification was into five classes: I. Pisces; II. Amphibia; III. Reptilia; IV. Aves; and V. Mammalia. As a matter of con- venience this classification will be followed here, though it is now usu- ally customary to substitute for the first class three — the Cyclostomata, lampreys and hags; Elasmobranchii, sharks, rays, etc.; and Pisces, the bony and other more or less typical fishes. The enormous importance of fishes as food and in other ways will be discussed later; a few of the ways in which the class is injurious to man will first be noted. Cyclostomes, Fig. Si. This low group of fishes, characterized by the circular, suctorial mouth, the absence of paired fins, the persistent noto- chord, and other primitive charac- ters, comprises the lampreys (Petro- myzon) and hags (Myxine; Bdello- stoma) most of which are marine and vary in size from 6 to 36 inches. In olden times lampreys (lamperns) were used as food; now they are seldom if ever eaten in this country and their chief importance is the damage they do to valuable food- fishes. The larger lampreys attach themselves to the bodies of other fish and, by the rasping action of PISCES ICQ gar lit? 110 ECONOMIC ZOOLOGY the horny teeth that cover the tongue and buccal cavity, they cut through the body wall and suck out the blood and soft parts until the victim dies; then they seek another host. Fish are sometimes found with one or more of these holes in the body wall, through which a loop of the intestine may protrude. In Cayuga Lake, New York, some years ago, serious damage was done the food-fishes by the large lake lampreys that were abundant there, so that a systematic warfare was carried on to exterminate the pests. The hags are parasitic in the same way upon marine fishes, except that they enter the body-cavity of the host through the hole they cut, and emerge again upon the death of the victim. Considerable damage is thus done the fishing industry in some regions. Elasmobranchs. — In this group are found the sharks and rays, which include the largest of all the fishes. Their value as food will be noted below; their negative importance will here be briefly described. In this connection the so-called man-eating sharks will at once come to mind. To what extent these monsters are dangerous to man is difficult to determine. There were fish specialists, a few years ago, who expressed great doubt as to whether man was ever attacked by any species of sharks, and it is probable that the majority of sharks are quite harmless, so far as attacking man is concerned. It is difficult to believe, however, that all the stories that are told in the tropics about man-eating sharks are fabrications, and it will be remembered that during the summer of 1916 there were several apparently authentic cases of loss of human life by sharks along the Atlantic coast of the United States; for example; the Baltimore Sun of July 7, 1916, had these headlines: "Shark Kills Bather. Bites off both Legs of Bellboy at Springlake, N. J. — Second Case in a Week. " While sharks of various species are common in the North Atlantic these visits from the man-eaters were very unusual and zoologists had various theories to explain the strange phenomenon. The shark that is usually called the "man-eater" is the Great White Shark, genus Carcharodon; this monster, according to Jordan, reaches a length of 25 feet; Giinther says it is sometimes 40 feet long and has been known to cut the body of a man in two at one bite. It is an inhabitant of tropical and subtropical seas, where it is much feared in some regions, by the water-loving natives. The other sharks, though they may reach a large size, are probably, as has been said, quite harm- PISCES III less to man, but are often injurious in other ways. For example, the small, dogfish sharks, Mustelus and Squalus, Fig. 82, are in many places very destructive to lobsters, crabs and various food-fishes, and to squid that are used for bait; they also seriously damage nets and other fishing gear. It is estimated that these dogfish cause a damage of at least $400,000 a year to the fisheries of Massachusetts. Other larger sharks though less common are often very destructive in the same way, as are the larger skates. It is not uncommon, in pulling a seine, to enclose a 6- or 8-foot shark that, in dashing to liberty, tears a great hole in the net that not only allows other fish to escape, but may take hours to repair. On one small sandy beach, of a few hundred FIG. 82. — Dog-fish, Squalus acanthias. yards length, on the coast of California, I once counted eight sharks of an average length of about 5 feet that had been drawn out of the sea in one morning by a group of fishermen who were seining there. On the same beach were often seen a considerable number of large rays that had been caught in the same way, and each of them had prob- ably caused some damage to the nets. It is no wonder that the fish- ermen despise these elasmobranchs. There are certain rays, known as sting-rays or "stingarees," in which the tail is armed with one or more spines, barbed on the sides and sometimes, in large species, 8 or 9 inches long. These rays are more common in warmer waters and are much dreaded by fishermen as they can, with a sudden swing of the tail, inflict an ugly wound that may be excruciatingly painful, or even, according to Giinther, cause death. The poison that enters the wound made by the spine may be merely in the mucus of the body or it may be secreted by a definite gland at the base of the grooved or hollow spine. 112 ECONOMIC ZOOLOGY Another formidable group of rays are the torpedoes or electric rays, Fig. 83. There are several species of the genus Torpedo, some of them 2 or 3 feet across; one of these large animals may, by a single discharge, disable an adult man, according to Giinther. The elec- tricity is generated in a pair of flat, curiously formed organs, lying on either side of the head. The electric organs are thoroughly enervated and are under the voluntary control of the ray. There are also electric eels that are cap- able of giving a powerful shock. Let us now notice several ways in which ' the elasmo- branchs are of positive economic importance. In many coun- tries, especially of the orient, the smaller sharks and some of the skates are used as food, either salted, dried or fresh. Some negro tribes are said to allow the flesh to decay before eating it. In America a sense- less prejudice exists against eat- ing sharks, but dogfish are now being canned and sold under a trade name and are a very agree- able addition to our list of food- fishes. In the markets of China small sharks are exhibited for sale the same as the ordinary food-fishes. ' Until the demand for this new food is much greater the excess of dogfish and other small sharks, captured by fishermen, can be used in making fertilizer. Therejte a limited demand for the smaller sharks by colleges and uni- versities for dissection purposes by classes in zoology. In China and India the fins of sharks and rays are extensively used for the production of gelatine and their collection is quite an important industry. Some of the larger sharks are useful sources of oil; a basking shark FIG. 83. — The torpedo or electric ray, Torpedo occidentalis. X/4- (From Dean, Fishes, Living and Fossil.) PISCES 113 may produce over a ton of this substance, which is obtained mainly from the liver. This huge fish may attain a length of over 30 feet. The skin of certain sharks and skates, armed as it is with sharply pointed, tooth-like scales, is sometimes used as a polisher of wood and other materials and is known as shagreen. Pisces. — Under this head will be noted some of the more impor- tant of the so-called teleost or bony fishes; the Dipnoans or lung-fish, which also belong in this group, tho extremely interesting zoologically, are not of sufficient economic importance to warrant discussion here. It is, of course, as food for man that these fish are chiefly important though there are some other ways in which they are economically im- portant. For example: the swim-bladder of the sturgeon and some other fish is used to make isinglass, fish-glue, mock pearls, etc.; the men- haden, a coarse kind of herring, is caught in seins by the ton and made into oil and fertilizer, several dozen fishing steamers being engaged along our coasts in catching them and conveying them to factories on shore; cod-liver oil is made from the livers of various species of cod- fish. The importance of fish as a food product is best appreciated by visiting a large fishery along the North Atlantic coast or on one of the great rivers of either coast. Along both coasts of the North American continents and in the Great Lakes there are thousands of small vessels constantly engaged in the catching of fish. On the Columbia River are the hugh salmon canneries and on the rivers of the east, are the fisheries for herring, shad, etc. Tens, possibly hundreds, of millions of dollars a year result from the fisheries of the United States. While most species of fish are suitable for food there are some that are poisonous either at all times or at certain seasons of the year. L. L. Mowbray (116) says: "Much has been said and written about the poisonous fishes of tropical and sub-tropical seas. It is a known fact that among people eating the same species and at the same time, even caught in the same locality, some have been poisoned, while others have not. Among fishes eaten by man, the species considered most likely to be dangerous as food during the season from May to October, are the barracuda, two species of kingfish, three species of jack, red rockfish and tiger rockfish." . . . " All these fishes are carnivorous, preying upon various species of fishes and invertebrates. There is no evidence whatever that they feed at any season upon forms which would 114 ECONOMIC ZOOLOGY render their flesh unwholesome." According to Dr. Geogaghan (116) once medical officer of the Turk Islands there are two forms of disease produced by these fish: one, like ordinary ptomaine poisoning, coming on 10 to 20 hours after eating the fish, acute but yielding quickly to treatment; the other producing slow dull pains, especially of the joints, coming on from 2 to 6 days after eating the fish and lasting many months. The same fish that cause these diseases in the Turk Islands and Bahamas are eaten at Key West and Bermuda where the poisoning is unknown. The reason for this Mowbray explains as follows: "After observing the conditions and manner in which the fish are handled, I have reached the conclusion that the reason they are poisonous, in one region and not in another, is that in Bermuda and Key West almost all fishing boats have live-wells, and therefore usually bring their fish to market alive, while in the Turk Islands and the Bahamas the fish are killed and allowed to remain in the sun until the shore is reached, sometimes 5 or 6 hours after they are caught. All of the fishes considered poisonous are of soft flesh and rich in gastric juices, and are therefore the most likely to decay quickly; and, when eaten in a partially decayed condition, cause ptomaine poisoning. Naturally, some are more poisonous than others. Those caught in the morning are exposed to the sun rays much longer, and are therefore much more decomposed." It would seem from this that possibly the poisonous character of fishes is largely a matter of their being more or less decomposed, though it is thought by some to be due to the character of the food eaten at different seasons. The most^ important of the world's food-fishes are said by some to be the herrings. This family (Clupeidae) includes considerably over 100 species and is probably more numerous in individuals than any other family of fishes. The common herring (Clupea harengus] is one of the most important of all food fishes; it is caught in nets in enormous numbers along the Atlantic coasts of both North America and Europe. For example at Port Deposit, Maryland, a fishing station on the Susquehanna River, these fish are caught in huge seines, hundreds of feet long, which are hauled in by an engine or by horse-power upon a floating dock; 100,000 fish may be brought in at one time in this way. They are cleaned, salted and packed in barrels on the spot so that they have no oppor- tunity to decay in the least. It has been estimated that at least 10,000,000,000 herring are caught annually by British and American PISCES 115 fishermen. There has been much uncertainty as to the habits of the true or sea-herring. It is supposed that there are numerous races, each of which swims in a separate school, sometimes in such enormous numbers that they form a closely crowded mass of from 5 to 20 square miles. These schools migrate from the deep sea toward the coasts where they spawn. • The river-herrings or alewives are the ones that were mentioned above as being caught in large numbers as they ascend the rivers of the Atlantic coast to spawn, they are largely smoked and salted. The shad, one of the finest of all food fishes, belongs to the herring family, and, like it, is caught in the rivers of the Atlantic seaboard, which it ascends for the purpose of spawning. Being a large, finely flavored fish it is usually eaten fresh, while the common herring is largely salted or smoked. The shad was successfully introduced into Cali- fornia, years ago, and is now abundant from Monterey Bay to Alaska. In spite of the fact that it is very prolific, an average female pro- ducing from 30,000 to 100,000 eggs, while many individuals produce several times that many, the shad has been largely reduced in numbers, with a corresponding rise in price. But for the work of the United States Bureau of Fisheries, to be discussed later, this delicious fish would probably have been practically exterminated. In 1900 this Bureau hatched and distributed 241,056,000 shad fry. Although, as noted above, shad produce eggs in enormous numbers, they are deposited more or less at random in the fresh water of the rivers, no nest is built and the percentage of loss of eggs is very high; added to this is the destruction by other fish and by man (who always catches them on the way to the breeding grounds), so that it is no wonder the industry was threatened with extinction. After spawning, the adults begin to feed again, and move toward the sea. The young shad remain in the rivers until about November of the first season when they are about 3 inches long; they remain in the sea for 3 or 4 years, till sexually mature, when the female may weigh from 3 to 6 pounds or more. The shoreward migration of shad depends upon the temperature of the water; it begins along the southern coasts and gradually extends northward as far as the St. Lawrence River. Another important member of the herring family is the sardine, the tiny fish characteristic of the Mediterranean Sea and presumably Il6 ECONOMIC ZOOLOGY named from the Island of Sardinia. The sardine is the most important fish of France. There are about 100 canneries for sardines, some of which have an annual output of 5,000,000 cans. There are various small species of the family Clupeidae that are known as sardines, the typical French species being the young pilchard, C. pilchardus. On the coast of California is a small fish, somewhat larger than the French sardine, that is canned in the same way in which the Mediter- ranean species is preserved, it is a true sardine, C. cacruteus. Eastport, Me., is the chief centre for sardines in the United States. The annual output of the canneries of Maine is about 550,000 cases, valued at about $2,000,000. The cod-fish (Gadus morrhua) is one of the most important of all the food fishes; it reaches a length of 3 or 4 feet and is characteristic of colder seas. As long ago as 1415 English fishermen sought the cod-fish on the coast of Iceland and since the sixteenth century they have been coming to the banks of Newfoundland. It is said that more than half the human population of Newfoundland get a living through the cod fisheries. It is also an important business in the North Atlantic region of the United States. Unlike the preceding the cod is caught with set-lines and hand-lines, rather than with seines, tho trap-nets are also used When brought to shore the fish are largely split open, rubbed with common salt, and then thoroughly dried by spreading them on platforms of boughs, known as " flakes,' ' in the sun. In good weather the fish will be cured in a week and is then hard and stiff. Each fish is turned over at least once a day so that both sides may be cured. The cod spawns at moderate depths and the eggs rise to the surface of the sea, where they remain till hatched. An average sized cod is said to produce from 2,000,000 to 4,000,000 eggs a year. The haddock is another well-known food fish belonging to the cod- fish family. The salmon family (Salmonidae) includes many of our finest, largest and gamiest food fishes, since besides the salmon proper, whose very name (from sa^io, to leap) indicates its active vigorous nature, the family includes various species of trout and white fish. While the trout are more popularly known to sportsmen and others, the great Quinnat or King Salmon of the Columbia River is economically, the most important member of the family, if not of all the fishes of the country. This magnificent fish, sometimes weighing 75 pounds, is PISCES caught as it enters the Columbia and other rivers of the Pacific coast by various mechanical contrivances; it is caught by the ton and is largely canned, on the spot. In 1908 the salmon fisheries were estimated at $10,500,000. This wholesale destruction of these animals on the way to their breeding grounds would doubtless long ago have seriously impaired the business but for the work of the U. S. Bureau of Fisheries. The remarkable life of this fish is too well known to need more than a mention here — how it leaves the sea as sexual maturity approaches, ascends the rivers, often for hundreds of miles, swimming rapids, jumping water-falls and overcoming astonishing obstacles until it reaches the quiet protected headwaters where the eggs may be deposited in safety; how the adults, wasted and torn by their long foodless journey, die without ever regaining their native ocean; how the eggs hatch into the tiny fish that gradually work their way down-stream, feeding as they go, until they reach the ocean as vigorous young salmon, able to dart about and escape the many enemies of the deep; and how these young salmon remain in the sea until they, in turn, have reached sexual maturity, when some mysterious impulse impels them to leave the ocean and ascend the rivers to certain death, that their kind maybe perpetuated. It is a wonderful illustration of the way nature often sacrifices the individual for the good of the race. Swordfishes, Fig. 84, are an interesting, though not a very important group. They are the largest of the teleost fishes sometimes reaching a length of 12 or 15 feet. The flat, blade-like snout which gives them their name is a very effective weapon, with which they are said to attack and kill whales; and it has been frequently reported that they have punctured the bottoms of small wooden boats, possibly mistaking them for their cetacean enemies, though why they should attack a whale at all is not clear. Swordfish "steaks" are a common article of diet in New England and elsewhere, and while perhaps not so delicate as some of the smaller fish, they are excellent food. A common method of capture of these large fish, which can cut their way out of an ordinary net, is to harpoon them from a small platform fixed on the bowsprit of a small sailing or power boat; it is a form of sport requiring both patience and great skill. The sturgeons, Fig. 85, are the largest of the freshwater fishes of the northern hemisphere where they occur. They may reach a length of 10 feet and are covered with hard, bony plates. Their flesh is used as n8 ECONOMIC ZOOLOGY food and their eggs, which are small and produced in enormous num- bers (one female, it is estimated, may produce 3,000,000 in one season) are made, especially in Russia, into Caviare. Besides this, from their air-bladder is made isinglass, as was noted above. Besides these few, hundreds of species of useful fishes might be mentioned, as there are probably but few that are not used as food by somebody, somewhere. ' FIG. 84. — Sword-fish (Tetraptu'rus), yellow-fin tuna, and yellow tail, caught with rod and reel at Santa Catalina Island. (From Dougherty, Economic Zoology, after Bulletin of B. of F., vol. xxviii, 1908.) Fish-culture. — The possibilities of fish-culture have been long recog- nized. This science was practised in early ages by the Chinese and later by the Romans. It was introduced into the United States about 1865; and in 1871 the federal government established the United States Fish Commission, now known as the Bureau of Fisheries. While the chief work of this Bureau is, perhaps, the artificial propagation of food PISCES 119 fishes, it also looks after the lobster, shell-fish, sponge and other industries dealing with aquatic life. It also controls laboratories for research at Woods Hole, Mass., Beaufort, N. C., and elsewhere. It owns several vessels equipped for deep-sea dredging and other lines of marine investigation; also several railway cars fitted with tanks, aerating pumps, living quarters for attendants, etc. which are used in 120 ECONOMIC ZOOLOGY transporting young fish from place to place. In 1901 the Bureau planted somewhat over 1,164,000,000 fish in waters of the United States. About Y± of these were whitefish and J£ were shad. Many of the individual States have their own fish commissions with numerous hatcheries conveniently located. In Europe there are, or were before the war, more than 400 fish hatcheries, more than half of which were operated profitably by private individuals; it is claimed that a profit of 1500 per cent, had been made in this work. The primary object of fish-culture is to increase the proportion of eggs that hatch and to protect the embryos and young fish until they have safely passed the perils, of early life and are able to take care of themselves. As in most animals the young fish are very helpless and, under natural conditions, easily fall prey to various enemies or are de- stroyed by unsuitable environmental conditions; the result is that the struggle for existence is extremely severe and the mortality enormous. Under the artificial conditions of the hatchery natural enemies of the young fish are excluded, and the environment is made as ideal as pos- sible without making it too unnatural. In nature the loss begins with fertilization. Where the eggs are fertilized in the open water of a pond or swiftly running stream it is obvious that many may easily escape coming in contact with spermatozoa; these of course will die and be lost. This loss is almost entirely avoided in the hatchery by the process of " stripping" and artificially mixing the eggs and sperm. In this process the male and female fish are carefully caught, at the time of sexual maturity, and stripped of their eggs and spermatozoa (roe and milt) by holding over a vessel and gently pressing out the roe or milt. Both fish must be ripe or fertilization will not take place. If ripe the belly of the fish feels soft and flabby, and if it be held up by the head the eggs will settle down toward the vent and almost run out without out- side pressure. If not ripe the belly of the fish feels firm and consider- able pressure must be exerted to strip out the eggs. The eggs are first stripped into a perfectly clean vessel with a small amount or even no water; then the milt is stripped into the same vessels and the mass gently shaken to insure thorough mixing of eggs and sperm. Fertilization takes place at once; after allowing the mass to stand for 15-20 minutes it is rinsed in clean water and transferred to the hatching trays. By this process from 90 per cent, to 100 per cent, of the eggs will be fertilized and an enormous saving over the natural method will result. PISCES 121 While in the hatching trays the eggs are examined frequently, and are sometimes stirred and rolled over with feathers; sometimes they are stirred by raising and lowering the trays in the water; and any eggs that escaped fertilization, or for any other reason have died, are carefully removed before they have time to mold or decay and infect the good eggs. A dead egg has a sort of opaque appearance that, with a little experience, is easily recognized. The hatching trays are of various types, a common form being a box about 15 X 24 inches and 6 inches deep made of galvanized wire netting. These trays, containing thousands of eggs, are usually placed in narrow, wooden troughs with a series of transverse partitions so arranged that the stream of water that passes through them is forced upward through the eggs in the tray and keeps them thoroughly mixed and aerated. The arrangement of trays, etc., varies at different hatcheries and with varying conditions. In a month or more, varying with the temperature of the water and other conditions the eggs hatch and the young fish, with the huge yolk sack attached, wriggle out of the trays and are taken care of until the yolk is absorbed and the fish are active and able to take care of them- selves if liberated into the waters of a suitable stream. While the yolk is still present the fish will not feed, but if they are kept longer they must be fed at frequent intervals on finely minced liver or other meat, great care being taken to prevent fouling of the water by uneaten scraps of meat. One of the primary factors in handling the eggs and young fish is cleanliness. Unless the water is of exceptional purity it must be led into settling tanks where the heavier sediment settles to the bottom and then it may be necessary to strain it through cloth to remove the finest particles of foreign matter that in the open streams, settles over the eggs and causes high mortality. Another factor is a free circulation of water in sufficient quantity to keep the eggs in motion and to keep them well aerated. It is often important that the temperature of the water be low during the season when hatching is in progress. When the young fish or "fry" have reached a proper size it is often necessary to transport them long distances to the place where they are to be liberated. For this purpose, as noted above, the Bureau of Fisheries employs several cars with tanks and aerating devices. The vessels most commonly used for handling the fry are the ordinary, large milk cans, holding about 15 gallons. The water in these cans must 122 ECONOMIC ZOOLOGY be kept cool, which in summer may necessitate the use of ice, and it must be either aerated or frequently changed. It is sometimes possible to keep it sufficiently aerated by dipping it out with a cup and pouring it back from some height. In some cases it is desired to ship the eggs to a distant point, where their further development will take place. This is done in various ways. In some instances, light wooden boxes are used and the eggs are packed as follows: a layer of damp material, preferably sphagnum moss, is placed in the bottom; over this a sheet of wet cheese cloth is spread upon which a layer of eggs is laid; over the eggs another sheet of cloth and another layer of damp moss are placed and this is repeated until a dozen or more layers are present, perhaps with a horizontal partition or two of wood to prevent too great pressure on the bottom eggs. This box is now packed in the centre of a larger box with dry moss or other shock-absorbing material and may be sent on a journey of several days' duration. In warm weather various methods are used to keep the eggs cool. The above is a brief account of the general methods of fish culture; the method varies with the different species of fish, with the locality, and with other varying conditions. There are many farms, remote from the coasts or from large bodies of water, where fresh fish are almost an impossible luxury. In many cases there are, or could be constructed, on these farms, large ponds, often used for the gathering of ice, where fish in sufficient numbers to supply the family could be raised at a nominal cost. If the pond be surrounded by a rank growth of vegetation it will support a considerable number of fish; if the pond be new or have a more artificial environment the fish will probably have to be fed. The kind of fish best suited to the pond will have to be determined by the local conditions. For ex- ample if the water be sluggish carp or cat-fish will have to be raised; if there be a fairly rapid circulation, changing the entire body of water every week, bass or perch may be kept; if the circulation be sufficient to change the water every day or two trout may be raised. The pond may be stocked with a few adults or by planting eggs or fry, which may probably, in most cases, be obtained from the nearest State hatchery or from the U. S. Bureau of Fisheries. Various bulletins upon the subject have been published that give specific directions. CHAPTER XI AMPHIBIA (BATRACHIA) As the name indicates this is a class of animals that have two modes of life, aquatic and terrestrial. The eggs are usually laid in water and hatch into fish-like tadpoles that may later give up their aquatic habits and live on land. Nearly all of them breathe by gills, in the larval condition, and many of them retain these gills through life, though lungs are usually present in the adult, sometimes being present in the same animal with the gills. The Amphibia, though so fish-like in many cases, are distinguished from the Pisces, by having pentadactyle limbs, usually without claws, in place of paired fins (where paired appendages are present at all) and by the absence of fin-rays in the median fins, where these organs are present. The skin is glandular and a bony dermal exoskeleton is sometimes present. There are also numerous character- istics of internal structures that need not be noted here. The Amphibia are interesting as illustrating the transition from water-breathing to air-breathing forms. The lower species retain their gills throughout life, while the higher forms lose their larval gills and breathe entirely by means of their lungs and skin. This metamor- phosis from the tadpole to the adult may take place in a few months or it may take a much longer time. Coincident with the disappearance of the gills and the development of the lungs the limbs usually make their appearance, the tail is absorbed, and other marked external and inter- nal changes take place, Fig. 86. As noted later, the tailed amphibia are very commonly confused with certain reptiles and called lizards; but they may usually at once be distinguished from the latter by the absence of scales and claws and by differences of habits, the former being usually found in dark, moist places while the latter prefer dry, sunny localities. There are fewer known species of living Amphibia than of any of the vertebrate classes, the estimates varying from about noo to 2200. With the, extinct forms we are not especially concerned since they can 123 124 ECONOMIC ZOOLOGY scarcely be said to have any economic value, except, perhaps, in the determination of geological horizons. As in other groups the classifica- tion of the Amphibia varies with different authors; the extinct forms are usually placed in two or three orders, the living forms in the following three orders: i. Apoda or Gymnophiona are legless, snake-like or worm- like forms found chiefly in the tropical and subtropical countries; 2. FIG. 86. — Metamorphosis of the frog. Tadpoles in different stages of develop- ment, from those just hatched (i) till the adult form is reached (8). 1-3, about life size; 2a, enlarged; 4-8, somewhat reduced. (From Hegner, College Zoology, after Mivart.) Caudata or Urodela are the tailed Amphibia, such as mud-puppies, sala- manders, etc.; 3. Salientia or Anura are the tailless forms, the frogs and toads. Of these three orders the last is by far the largest and the first the smallest. In cold regions the amphibia hibernate through the se- vere winter weather by burying themselves in the ground or in the mud and leaves at the bottom of ponds and streams. Being inoffensive AMPHIBIA (BATRACHIA) 125 creatures they depend for protection upon their activity, their protec- tive coloration and in some cases, upon poison glands in the skin. Many of them have considerable power of regenerating lost parts. PIG. 87. — Mud puppy or water dog. Necturus maculatus. X;H}. FIG. 88. — Hellbender or "Alligator, " Cryptobranchus allegheniensis. Although not one of the more important groups economically, prac- tically all of the Amphibia are of some value to man, and few if any are more injurious than beneficial. 126 ECONOMIC ZOOLOGY Of the Apoda little need be said; although they feed on worms and in- sect larvae, they are not numerous enough to be of great importance. The Caudata which are represented by several more or less popularly known species are probably of considerable value as destroyers of in- sects. Even the smaller salamanders, Fig. 89, that are more numerous than is commonly supposed because they are largely nocturnal and secretive in habits, doubtless destroy many insects, both adult and larval. Some of the larger forms like the common mud-puppy (Nec- turus), Fig. 87, and the hellbender (Cryptobranchus), Fig. 88, are also FIG. 89. — Spotted salamander, Amblystoma punctatum. X M- (From Surface, First Report on the Economic Features of the Amphibians of Pennsylvania.) useful as scavengers in our streams, though they sometimes are a nuisance to fishermen by taking their bait. Although the writer has made but few experiments there seems to be no reason why these larger salaman- ders should not be used as food. Their flesh looks as attractive as that of the frog and in a two-foot giant salamander (Cryptobranchus) there is a considerable mass of flesh, especially in the tail, in a full grown Necturus also there is a considerable quantity of flesh which is very palatable. The Anura are by far the most important, economically, of the Amphibia. Of the various families of this order three will be noted: AMPHIBIA (BATRACHIA) 127 the Hylidae or treefrogs, the Ranidae or true frogs and the Bufonidae or toads. The Hylida, Fig. 90, are usually small forms; they are arboreal in habits, as the name indicates, and as an aid in climbing have adhesive disks at the ends of their fingers and toes. They have remarkable vocal powers, due partly to the presence of a large vocal sac. Of the nearly 200 species, more than a dozen are found in North Am- PIG. 90. — Tree frog, sp. Xi. Note discs on toes. erica. Though doubtless of less importance than the other Anura, these small frogs probably destroy large numbers of harmful insects. The Ranidce, of which there are more than 250 species, more than a dozen of which occur in the United States, are useful as destroyers of insects, as subjects for dissection and experimental work, and es- pecially as an article of diet. Almost any of the true frogs may be used as food, though many people think that only the bullfrogs are edible. A simila r mistaken idea pre- 128 ECONOMIC ZOOLOGY vails in the belief that only the hind legs can be eaten, as a matter of fact many persons, after, skinning, cutting off the head and eviscerating, fry the entire body, perhaps in egg and bread-crumbs, perhaps without. The main muscles, of course, are those of the hind legs, but there is no sense in wasting all the rest of the body. Of our native frogs the common bullfrog, Rana catesbiana, Fig. 91, is the largest and most generally known as an article of diet; it may reach a length of 8 inches and its deep, bull-like roar is a familiar FIG. 91. — Common bullfrog, Rana catesbiana; male. (After Chamberlain, Edible Frogs of the United States.) sound to those living in the eastern half of the North American con- tinent. In the adult condition its larger size and massive, clumsy shape will distinguish it, ordinarily, from the other common species, as will the presence of a fold of skin that arises back of the eye, passes over the tympanum, past the insertion of the foreleg, to disappear on the chest; the complete webbing of the hind toes and the absence of the dorsal folds of skin will also serve to distinguish it. The color is quite variable but there is apt to be a considerable amount of deep green above and of yellow beneath. There are two species of western frogs that are found along the coastal States; they are not so well known as the common bullfrog. AMPHIBIA (BATRACHIA) 129 A frog somewhat similar to the bullfrog, both in appearance and in habits, is the green or spring frog, R. clamata, Fig. 93; it is much smaller in size, however, the adult measuring only 3 inches. Instead of the deep bellowing it has a note that may be represented by the words, " chock, chock, chock," and an occasional single note "chung. " It is, in many places the first species heard in the spring. It is more or less solitary in habits and seldom leaves the water. Like the preceding species it passes the first winter in the tadpole stage. The most widely distributed of our frogs is the common frog, leo- pard frog, spring frog or shad frog, R. mrescens, Fig. 92. It is found over practically the entire continent east of the Sierra Nevada Mountains. It reaches a length of 3^ inches and is distinctly marked PIG. 92. — Spring or leopard frog, Rana virescens. (After Chamberlain, Edible Frogs of the United States.) on the back and sides and legs with dark, rectangular blotches bordered with white or yellow. A glandular fold runs from the eye, along the dorsal part of the side to the posterior part of the body. The pickerel, marsh, or tiger frog, R. palustris, closely resembles the leopard frog from which it may be distinguished by the bright yellow on the legs. It is the most active of the frogs and is seldom eaten. Though preferring cold streams, it is often found in grass; it is rather solitary in habits. The flesh of frogs is best in the fall and winter. Later in the season, after prolonged hibernation, the body is more or less emaciated. Frogs are collected for the market in large numbers in California, Missouri, Arkansas, Indiana, Ohio, Maryland, Virginia and New York, 130 ECONOMIC ZOOLOGY especially in the last, also in Ontario and other parts of Canada. They are sold alive and by the pound, dressed, the price varying with the locality, season and other conditions. Frogs are collected in various ways — a hook and line, baited with a piece of red cloth is sometimes dangled in front of the frog who seizes the moving cloth and is thus hooked; small bore fire arms and various spears are also used, sometimes at night with a bright light to dazzle the eyes of the frogs; sometimes they are dug out of the mud where they are hibernating. Unrestricted hunting has, in some localities, nearly exterminated the frogs and has brought up the subject of their artificial propagation. Without sufficient knowledge of the breeding habits of frogs it would seem that, with the high market values usually prevailing, it should be an easy matter to make large profits by raising them for market. Part of the process is quite easily handled, but, as we shall see, there is one peculiarity in the habits of frogs that is difficult to meet. Every- one is familiar with the masses of frog eggs that are seen in small ponds and sluggish streams in the early spring; these may be collected in al- most unlimited numbers. In a few days or weeks, depending upon the temperature of the water, these eggs hatch into tiny tadpoles that soon begin to feed voraciously upon any kind of organic material that may be available and to grow rapidly. During the tadpole stage there are many enemies such as birds, snakes, turtles, crawfish and adult frogs, that destroy these larvae in large numbers so that the first problem of the frog culturist is to protect in some way the eggs and tadpoles. This may be done by collecting the eggs and allowing them to hatch and develop in artificial ponds or tanks where the tadpoles may be fed and protected, or better, perhaps by screening small natural ponds with wire netting to keep out the above-mentioned enemies and stocking these ponds with a number of adult frogs, males and females, to lay the eggs. In this way tadpoles without number may be raised, but the main difficulty mentioned above, arises when the tadpoles change to frogs, which happens in from two months to two years. It is essential that when this transformation takes place that the young frogs or old tadpoles, whichever they may be called, Fig. 86, have a sloping shore where they may crawl out on the bank, otherwise the metamorphosis is indefinitely postponed; tadpoles have been kept in aquaria for several years without transformation because of lack of a place for them to leave .AMPHIBIA (BATRACHIA) 131 the water. The difficulty that arises is that while the tadpole would eat anything the frog will eat nothing that is not moving. A dead insect on the ground will remain untouched; one that is drifting along on the surface of the pond will be seized and eaten. Here, then, is the stum- bling block to the frog culturist, to supply living food to the numberless young frogs that he has obtained so easily. Various methods have been tried. For example meat was strewn on the shore and allowed to decay with the idea that it would attract flies and other insects for the frogs, but the decaying meat is apt to foul the water and kill the young FIG. 93. — Green or spring frog, Rana clamata. (After Chamberlain, Edible Frogs of the United States.) frogs and tadpoles. The only practicable method seems to be to use natural ponds whose banks are covered with a rank growth of vegetation that will supply the necessary insects. Such a pond should be partly shaded and, of course, must not dry up as summer progresses. In this way, by aiding nature somewhat, frogs are successfully raised at a number of places; for example in Ontario such a farm has been in operation for 25 years, producing in one year as much as 5000 pounds of dressed legs and 7000 living frogs. 132 ECONOMIC ZOOLOGY It usually requires three or four years for frogs to reach maturity and it is generally supposed that they may live for 15 or 20 years. One danger to eggs and tadpoles that cannot well be eliminated by frog culture is from late cold spells that may freeze the shallow pools and kill large numbers of the inhabitants. The Bufonidce include over a hundred species of toads belonging chiefly to the genus Bufo; over a dozen representatives of this genus have been found in North America. The common toad of the eastern United States, Bufo lentiginosus Americanus, Fig. 94, is familiar to all as the clumsy, warty animal that, FIG. 94. — The American toad, Bufo lentiginosus americanus. X%. after hiding in some dark nook all day, hops out, toward dusk, to seek his food during the night. Being an ugly animal the toad, in olden times was considered highly venomous, as noted by Shakespeare and other more ancient writers, and a remnant of these superstitions is seen even now in the very common and entirely erroneous belief that warts may be caused by handling toads. As a matter of fact, however, the glandular warts so characteristic of the toad do secrete a substance that protects them quite largely, from being eaten as are the other members of the Urodila, though the flesh is said not to differ appreciably in taste from that of the Ranidae. AMPHIBIA (BATRACHIA) 133 While the adult toad is primarily a land animal and hibernates in some cavity under ground, usually in groups, it seeks the pools in early spring to spawn as do the rest of its class, laying the eggs in long, easily recognized strings, instead of in masses; 1200-1500 may be laid by a single female. During the breeding season the toad's call may be heard as a pleasant, tremulous trill, lasting usually about 5 or 10 seconds. The development is about the same as that of the Ranidse. It is said that sexual maturity is not reached until the fourth year. Much has been conjectured and written about the age to which toads may live but nothing very definite seems to be known; it seems likely that they may live for 20 years or more. Of the familiar stories of toads being found in the centre of rocks little need be said; a little common sense will show the absurdity of supposing an animal could re- main alive during the thousands or millions of years that must have elapsed since such rocks were laid down as sand or mud. A number of actual experiments have been tried to test this oft-repeated tale; toads were buried in cavities in the centre of plaster-of-Paris blocks and in sealed cavities in rocks of various sorts; none of the toads lived more than two years, and while it is surprising to find any animal living so long without food and water, two years is an infinitesimal time com- pared to the age of rocks. The numerous recorded cases of these rock-encased toads are doubtless to be explained as errors of observation or as pure fabrications. As has been said the toad feeds largely at night, in towns often col- lecting under the electric lights and eating the insects that fall to the ground in large numbers at such places. Kirkland, who has carefully studied the feeding habits of the common toad, makes some interesting observations. He says the toad's food is about 88 per cent, insects, and 1 6 per cent, of these are cutworms; counting these destructive cutworms alone he estimates the annual saving to the farmer by each toad as nearly 20 dollars. He finds that the toad eats four stomach- fulls every 24 hours; in three months this will amount to about 10,000 insects, a majority of which are injurious; slugs, myriapods, etc., are also eaten; in fact any moving animal of suitable size, even stinging bees, are snapped up by the lightning-quick, sticky tongue. By confin- ing a toad in an open box with syrup or other sweet substance to attract insects its methods of feeding may be studied in an interesting way. 134 ECONOMIC ZOOLOGY By watching the live toads and by examination of the stomach con- tents of others, Kirkland collected valuable data in regard to their food at different seasons and under different conditions. For example during a pest of army worms he found in one toad's stomach 55 of the worms; at another time he found 65 larvae of the gypsy moth in one stomach; and in another toad were found 37 tent caterpillars. These and many other figures might be given to show that as an in- sect destroyer the toad probably has few superiors and that it is, perhaps, quite as valuable as the average bird and should be equally protected by law. They are useful not only in gardens but may be kept in green- houses. In a certain greenhouse in Massachusetts a valuable collection of orchids was saved by the introduction of a number of toads. They should be collected and brought into gardens, as is done in France, and a number of boards or stone shelters provided for them to creep under and escape the heat of the sun. Probably if the garden were pro- vided with a small pond of running water they would breed there and greatly increase their numbers. They frequently take up more or less permanent summer quarters under porches and other places to which they return every morning after the night's hunt. Their chief enemies are hawks, crows, and snakes and from these they could be protected, more or less, in gardens. Chickens and ducks also are destructive to the young toads; and the ubiquitous small boy who, unless otherwise educated, is an enemy to all living things, is also prone to kill toads of all ages. Fortunately the toad is not used as an article of human food, so that the pot-hunter, the worst of all enemies of the lower animals, does not trouble him. It will be seen, then, that practically all of the Amphibia are of some value to man and that few if any of them are harmful in any way. CHAPTER XII REPTILIA Reptilia are cold-blooded vertebrates with an epidermal skeleton of scales, and often with an armor of bony dermal plates. They never breathe by gills and do not have the tadpole stage seen in the Amphibia. Many of them lay eggs of a large relative size, inclosed in a leathery or a calcareous shell. The centra of the vertebrae have spheroidal articu- lar surfaces. There is one occipital condyle and the mandibles usually, and other bones frequently, bear teeth. The ventricles of the heart are usually incompletely separated and there are always two aortic arches in the adult. The reptiles, though clearly distinguished from them by having cold instead of warm blood and scales instead of feathers, are closely related to the next class, the birds, with whom they are frequently grouped under the name Sauropsida. In the same way the reptiles, birds and mammals, since they all possess the embryonic structure known as the amnion, are ground together under the name, Amniota. During the Mesozoic period the. rep tiles reached their maximum, both as to numbers and individual size, so that this period is often spoken of as the "age of reptiles;" the largest of the living reptiles are pygmies compared to the huge individuals of this age. The reptilia are variously classified by different authors, being di- vided into from nine to fifteen or more orders. Of these orders, four include the 4000 or more species of living forms, which, of course, are the only ones of economic importance except as mere specimens, or as determiners of geological horizons. The four orders of living reptilia are as follows: i. Chelonia or Testudinata. — These forms are easily recognized by the bony or leathery carapace covering the dorsal side of the body and a flat plastron on the ventral side; these bones are usually covered with horny epidermal plates; the appendages are clawed and adapted for use on land, or are paddle-like for use in swimming. The jaws are armed with sharp bony edges instead of teeth; tympanic membranes 136 ECONOMIC ZOOLOGY and movable eyelids are present. These are the familiar and easily recognized turtles, terrapins and tortoises. 2. The Squamata. — The characteristics of this order, as a whole, are largely osteological so that we shall consider at once the two sub- orders of living Squamata, which are sometimes considered as distinct orders; they are the Lacertilia and the Ophidia. The former are usually provided with legs for walking; nearly always with eyelids and tympanic membranes; the rami of the mandibles are closely united at the sym- physis and the mouth can open only moderately widely; a sternum is present; they are represented by the various lizards, such as Geckos Iguanas, Chameleons, etc. The latter sub-order, the Ophidia, are the snakes they are much elongated forms without appendages, movable eyelids, tympanum and sternum; the rami of the mandibles are con- nected by elastic fibres, and the mouth can be opened to an extraor- dinary width. 3. The Crocodilia. — The body is here more or less covered with bony scales; a sternum is present and also a set of abdominal ribs: the Cloaca is longitudinal in position and sheaths a medium penis; the legs are adapted for walking and the tail is usually compressed for swimming; the teeth are numerous and held in sockets; the ventricle of the heart, in living species, is completely divided. This order in- cludes as living representatives the familiar crocodiles and alligators and also the gavials and caimans, some of which are the giants of the present reptilian world. 4. Rhynchocephalia. — This order is represented by a single living genus Hatteria or Sphenodon; a lizard-like reptile found in New Zealand. Since its only economic importance is as a specimen no further description will be given here. Chelonia or Testudinata. — The Chelonia are, by some, divided into three groups, the turtles, the terrapins, and the tortoises, this division being based chiefly upon the habitat of the species, whether terrestrial, aquatic or amphibious. As these names are employed differently by different authors and in different sections of the world, no attempt will be made here to distinguish between them, and the word turtle will be generally used for any member of the order. It is as food for man that the chelonia are chiefly important, though there are other economic aspects of the group that will be briefly discussed. REPTILIA 137 Turtles are used for food over practically the entire world, but, it is said, their flesh is forbidden to Mohammedans, and is abhorred by cer- tain Greeks. Nearly, if not all, species may be eaten, but there is, of course, much difference in the quality of the flesh, and Surface (136) states that during a strike of miners in eastern Pennsylvania many of them were made sick by eating turtles, supposedly the box tortoise, so that the common idea that this form is inedible, at least at certain seasons, is probably correct. There are also a few species whose offensive odor makes them undesirable as food. It is said that even the flesh of the Green Turtle, about to be described, is poisonous at certain seasons of the year in some countries where it is found. The Green Turtle, Chelone mydas, Fig. 95. — This is, perhaps, the most important of the turtles as an article of food; it is an important article of commerce, and is an important part of the diet of some of the tropical peoples. It is found in tropical and semitropical seas through- out the world, and may reach a weight of 500 pounds, though these huge ones are not so good for food; those found in markets usually weigh from 50 to 75 pounds. The name has been given because of the green color of the flesh. Jamaica was formerly, and perhaps still is, one of the chief centres for the Green Turtle industry; Key West has also been an important centre. In one year 15,000 animals were received into England, besides a large amount of dried meat in cans, the meat for canning being cut into strips and dried in the sun, where it acquires almost the consistency of glue and requires long soaking in water before it is fit for food. About 1900 the turtle trade of Jamaica amounted to about $50,000, and the demand was greater than the supply. As in many other turtles the oil may be extracted and used for culinary purposes in place of butter or olive oil. In markets these turtles are kept lying on their backs not only to keep them from escaping but because, being adapted to life in the water, they would not be able to breathe if laid upon a hard surface, right side up; their plastron is not firm, like that of a land form, and the weight of the animal, when not supported by the surrounding water, so com- presses the internal organs that suffocation may be produced. The flesh may be cooked in various ways, and is said to be very digestible. The Green Turtle lays from 200 to 300 leathery-shelled eggs that are 138 ECONOMIC ZOOLOGY REPTILIA 139 more nutritious than hen's eggs; a dozen of them may be eaten at once. The eggs, which are carefully buried and concealed by the female, are found by prodding in the sand, along the shore, with a sharp stick. Owing to the decrease in their numbers it has been suggested that these turtles be artificially propagated; it is thought they would reach a marketable size in three years. Along the Amazon and Orinoko Rivers the eggs of various turtles form a very important article of food; they are preserved by rolling and packing in salt, an