Abstract
Synthetocaulus rufescens produces extensive lung lesions and is economically one of the most important lungworms; consequently a study of the intermediate host was undertaken.
The body of the embryo is small and filariform. The cuticula shows very fine transverse striations. The width of the body is 16-20μ near the centre of the bodily length. Both extremities are gradually tapered. Near the head it is reduced to 8.3μ. The entire embryo measures from 300 to 325μ. The oesophagus measures about 145μ and shows 2 bulbous enlargements corresponding to the embryo of other lung-worms. The opening of the excretory duct is located 87-95μ while the genital rudiment is situated about 200μ from the tip of the head. The intestinal tube breaks through the cuticula 40-42μ from the tip of the tail. The tail is slightly curved and is separated and recognized by a very small dorsal indentation. It is without any appendix on the back.
Biology and Morphology of the Larvae. The viability is the same as that of the embryos of Mullerius capillaris. They are rapidly killed by complete desiccation. In clear water they remain alive for more than one year. In artificial culture the presence of infusoria is of little consequence, while rotifera may destroy the embryos in a few days.
Continuous observations for indefinite periods never reveal changes in the structure of the embryo in the free state or any indications of a transformation into the larval stage. Obviously the embryo has to pass through an intermediate host. In former publications it was shown that the development of the Synthetocaulus is completed in several species of snails which act as intermediate hosts. Protostrongylus (Synthetocaulus) rufescens probably develops in a similar manner.
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