1907.] NATURAL SCIENCES OF PHILADELPHIA. 277 



Deviations from these two types of development are not uncommon, 

 some of the more striking variations being slunvn in figs. 2-i-.31. The 

 spore from which fig. 24 was drawn seems to be a variation of Type I, 

 in which the nuclei have moved into the cytoplasm instead of towards 

 the outer border of the vacuoles. It is possible, as I have already 

 suggested, that fig. 24 shows a normal stage in the development of the 

 spore, and that it belongs between the stage of fig. 12 and that of fig. 

 13. In the spore shown in fig. 25 it is evident that, when the vacuole 

 divided, both nuclei remained in one of the two vacuoles that were 

 formed (as is shown in fig. 28), and that they passed into the cytoplasm 

 after the vacuole had taken its position at the end of the spore. As 

 indicated in fig. 25, the cytoplasm surrounding the nuclei stains con- 

 siderably darker than that in the rest of the spore; and although the 

 nuclei are clearly seen at this time, they are totally obscured in the 

 following stage when the region in which they lie stains black (fig. 26). 

 A spore in which one nucleus only has left its vacuole is shown in fig. 27 ; 

 while variations in the number, size, and situation of the vacuoles are 

 shown in figs. 28-31. 



I can offer no explanation as to the way in which the cells of Bidder's 

 organ become infected with the parasite. There is no direct means of 

 communication betw^een this organ and the testis, and therefore it 

 does not seem possible that infection was through the cloaca and the 

 kidneys, hence by way of the testis to Bidder's organ. As Bidder's 

 organ contains a large number of capillaries, it seems most probable that 

 infection took place through the blood. Although I have^carefully 

 examined sections of the blood vessels containing large numbers of 

 corpuscles, I have found no traces of the parasite either in the corpuscles 

 or in the plasma. In one instance three mature spores were found in 

 the plasma of a capillary in Bidder's organ ; but it seems probable that 

 these spores were derived from one of the many cysts in the organ con- 

 taining ripe spores. As all of the large ova in Bidder's organ eventually 

 degenerate, usually through the rupture of the outer wall and the 

 penetration of a capillary into the interior, it is evident that the spores 

 finally get into the circulation. How they pass to the exterior and 

 whether they subsequently undergo a further development in another 

 host remains to be determined. 



During recent years much interest has been taken in the life history 

 of the Sporozoa which seem to infect many of the invertebrates as well 

 as all classes of the vertebrates. Interest in this group has naturally 

 centred in the parasites infecting the mammals ; and the amphibians as a 

 class have not been systematically examined, either in Europe or in 

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