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cells. In both there are certain problematic cells between the granular 

 body and the ciliated ectoderm. That the infusoriform should be bilate- 

 rally instead of radially symmetrical, and have only two huge cells con- 

 taining large refractive bodies instead of many small ones with small 

 refractive bodies is no serious obstacle to the comparison. The granu- 

 les in the central body of Rhopalura are true flagellate spermatozoa as 

 Metchnikoff (1881) has shown, although Julin (1882) was less suc- 

 cessful in resolving them. I have had no better success than van 

 Beneden in making out flagella to the granules in the urn-contents 

 of the infusoriform. Van Beneden, however, believes that he has 

 seen a ciliary movement in the urn. The contents of this mysterious 

 organ are discharged by the infusoriform after it leaves its mother. In 

 the Californian species the infusoriform rarely remains within its mother 

 till the small nuclei of the urn-contents are reduced to granules, so I 

 am inclined to believe that the spermatozoa, if spermatozoa they really 

 be, must mature while the infusoriform is swimming about. 



3) The signification of the infusorigen is even more obscure than 

 that of the infusoriform. It has been regarded as an embryo (epibolic 

 gastrula) the ectoderm cells of which are all germ-cells and give rise 

 to the infusoriforms. On this supposition Dicyema performs on its 

 offspring an experiment which some experimental embryologists would 

 regard as impossible, since in this case the gastrula is resolved into its 

 component cells each of which is capable of reproducing a whole or- 

 ganism. I believe that the infusorigen may admit of a different inter- 

 pretation. I find both in sections and in Dicyema mounted 

 in toto, a number of very deeply staining granules mingled 

 with and adhering to the cells of the infusorigens. These 

 granules closely resemble the minute bodies contained in 

 the urn of the mature infusoriform and may therefore be 

 spermatozoa. If this is the case, the central cell of the infusorigen 

 may represent a chemotactic center which facilitates fertilization by 

 holding all the germ-cells together in a mass and by attracting the 

 spermatozoa to the same point in the axial cell of the Dicyema. On 

 this interpretation the male Dicyemids would arise from fertilized, the 

 females, or nematogens from unfertilized ova. 



In conclusion I will give the life-history of Dicyema as suggested 

 by the preceding considerations. Both the female (nematogen) and 

 the male (infusoriform) may migrate from one Octopus to another. One 

 or more nematogens probably enter the kidney soon after the Octopus 

 is hatched and these multiply paedogenetically till the surfaces of the 

 venous appendages are tufted with nematogens. After a time partheno- 

 genesis languishes, the germ-cells being no longer able to produce 



