鶏に寄生する有輪絛虫の生活史
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概要
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The life-history of Raillietina cesticillus living on a chicken has been studied well, for cestodes are prevalent all over the world. At present, 17 genus, 35 species, of their intermediate hosts are found in Europe and American. In Japan, they belong to common cestodes, but the writer has never found any references dealing with the life-history of them. This paper describs the movements of the segments and the life-history of the cestodes. They injure their hosts by destroging the tissue of the small intestinal wall, thrusting deep their scolex into its wall, still more entering the muscularis mucosa, and forming intestinal nodules. There are many groups of white Leghorn chickens of 2 years old in the hen-house of Nara Agricultural Laboratory, and many of them are infected with R. cesticillus. Many gravid segments are found on new feces and many insects gather on the feces to eat the gravid segments.(1) Behavior of gravid segments. Most gravid segments of the excreted R. cesticillus are connected into 4-5 segments. They creep about freely on the surface of the new feces. The description of their movements were made by REID, ACKERT and CASE in 1938. When feces are excreted on the ground, the segments move to the edges of moist parts made by the excrements, or to the dark parts of the feces and also to dry sand granule in the circumference of them. In other words, their movements show any tropism against light, heat or gravity. The process of their movements are illustrated in Fig. 1. When their movements stop, the conective segments are separated into a single segment and each segment changes into a milkly white sperical mass.(2) Natual infection of Tachys laetifius. In order to find the intermsdiate hosts of the cestode, the writer collected the following 6 species of the insects ; Tetramorium caespitum jacoti WHEELER, Euponera solitaria, Tachys laetificus BATES, Bcmbidion mcrawiti CSIKI, Euborellia pallipes SHIRAKT, Onthophagus atcr WATERHOUSE, from April to September 1951, which were found in the experimental chicken yards mentioned already. By examining whether the above mentioned insects were infected with cysticercoid or not, the writer found that only Tachys laetificus were naturally infected. The dissection of 125 Tachys laetificus, led me to find the fact that 45 beetles (36%) were infected with cysticercoids. The avarage number of cysticercoids found in one insects were 4.4 and the maximam number was 19.(3) Forms of onchosphere and cysticercoid. The egg (Fig.2) of R. cesticillus is about 92-ll9μ long and 72-108μ wide the onchosphero having four membranes is recognized in center of the egg. The onchosphere is about 3l-53μ long and 38-46μ wide and has six embryonal hooks. The middle two hooks (Fig.2.D.) are about 21μ and the lateral four hooks (Fig. 2. E.) 17μ in length. Tachys lactificus, having eaten the onchosphere, begin to grow in the abdominal cavity of the insect and develop into mature cysticercoids. Their developmental process is illustrated in Fig.3. The mature cysticercoid (Fig. 4) is approximately elliptical and has a larval scolex invaginated in the bladder, which is entirely surrounded by a heavy cyst wall. Neither caudal appendage, a embryonal hook, nor sucher is ackowledged on any of the specimens examined. The size of cysticercoid is 327-489μ long anp 267-337μ wide.(4) Experimental infection of chicken. The writer succeeded in infecting chickens by feeding them cysticercoid taken from Tachys laetificus. That is, the writer examined chicken No.1 and No.2 on Aug. 20, 15th day after the infection ; No.3, No.1, on Aug.25, 20th day after the infection and found parasites of R. cesticillus in the small intestines. The percentage of infection of the cysticercoids in tapeworms was 73.8%. As for the controlbirds, kept side by side the experimented birds, they were found negative by the post-mortem examination. Thus the writer could ascertain that Tachys lactificus was the suitable intermediate host for this tapeworm.
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