ACANTHOCEPHALA EMBRYOLOGY 



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fertilised whilst floating in the. fluid of the body-cavity. The 

 eggs segment and the embryo is formed 

 whilst still in the body of the mother. 



The embryos escape by means of a 

 complicated apparatus the details of 

 which vary in the different species, but 

 which, like many of the organs in these 

 animals, consists of very few cells with 

 very large nuclei. This apparatus con- 

 sists of three parts : the bell, the uterus, 

 and the oviduct. The bell is a large 

 funnel-shaped structure, which opens 

 into the body -cavity, and is connected 

 with the end of the ligament ; near its 

 lower end, where it is continuous with 

 the uterus, is a second smaller opening 

 situated dorsally. By the contraction 

 and expansion of its lips the oval embryos 

 are swallowed and pass on through the 

 uterus to the oviduct, which opens at the 

 posterior end of the body. If the bell 

 takes in any of the less mature eggs 

 which are spherical in shape, they are 

 passed back into the body-cavity through 

 the above-mentioned dorsal opening, and 

 the same orifice permits the passage of 

 the spermatozoa even when the bell is 

 full of embryos. 



Embryology. After fertilisation the 

 egg surrounds itself with several egg- 

 shells, three of which are usually dis- 

 tinguished; the embryo is already far FlG . 97 ._ An egg of 

 advanced in its development by the rhynchm aa<s Rud. sur- 

 time it leaves the body of the mother 

 and passes out into the alimentary canal 

 of the Vertebrate host. It leaves the 

 body of this second host with the faeces, 

 and is eaten by the first or larval host, 

 usually a small Crustacean or water-insect, but in some cases a 

 fish, within whose alimentary canal it casts its membranes and 



rounded by three egg-shells. 

 Highly magnified. The 

 egg has segmented, and the 

 cells are differentiated into 

 a, the entoblast, and b, the 

 ectoblast ; c, spines. (From 

 Hauiauu.) 



