By E. van Beneden[54] they were observed in a Teleostean ovum to appear nearly simultaneously in considerable numbers in the granular matter beneath the blastoderm. Van Beneden concludes from the simultaneous appearance of these bodies that they develop autogenously. Kupffer at an earlier period arrived at a similar conclusion. My own observations on these nuclei in Elasmobranchii on the whole support the conclusions to be derived from Lankester's, Kupffer's and Van Beneden's observations. As mentioned above, the nuclei in Elasmobranchii do not appear simultaneously, but increase in number as development proceeds; and it is possible that Van Beneden may be mistaken on this point. No evidence came before me of derivation from pre-existing nuclei in the blastoderm. My observations prove however that the nuclei increase by division. This is shewn by the fact that I have found them with the spindle modification (fig. 46, _nx´_), and that in most cases they usually exhibit the form of a number of aggregated vesicles[55], which is a character of nuclei which have just undergone division. It should be mentioned however that I failed to find a spindle modification of the nuclei in the later stages. Against these observations must be set those of Bobretzky, according to which the nuclei in Oniscus are really the nuclei of cells which have migrated from the blastoderm. Bobretzky's observations do not however appear to be very conclusive. [54] _Quart. Journ. of Micr. Science,_ Vol. XVIII. p. 41. [55] At the time when my observations on Elasmobranchii were carried out, this peculiar condition of the nucleus had not been elucidated. It must be admitted that the general evidence at our command appears to indicate that the nuclei of the yolk in meroblastic ova originate _spontaneously_. There is however a difficulty in accepting this conclusion in the fact that all the other nuclei of the embryo are descendants of the first segmentation nucleus; and for this reason it still appears to me possible that the nuclei of the yolk will be found to originate from the continued division of one primitive nucleus, itself derived from the segmentation nucleus. The existence of these nuclei in the yolk and the formation of a distinct cell body around them is a strong piece of evidence in favour of the view above maintained, (which is not universally accepted,) that the part of the ovum of meroblastic ova which does not segment is of the same nature as that which does segment, and differs only in being relatively deficient in active protoplasm. The following forms have meroblastic ova of the first type: the Cephalopoda, _Pyrosoma_, Elasmobranchii, Teleostei, Reptilia, Aves, Ornithodelphia (?). The second type of meroblastic segmentation occurs in many Crustacea, (parasitic Copepoda, Isopoda _Mysis_, etc.). It is also stated to be found in _Scorpio_.