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The accounts dealing with developmental stages of Amphipholis squamata present what must be one of the most confusing series of incompatible statements in the whole of echinoderm embryological literature. From the first it became apparent that its development was quite unlike that of other ophiuroids. Research on its embryology was initiated in 1842 when Quatrefages discovered that the species is viviparous. He communicated his result to Milne-Edwards, who recorded it in a paper. In 1851 Krohn discovered the existence during part of the development of an embryonic attachment to the parent (or “Nabelschnur”), and in the same year Schultze discovered the transitory larval skeleton. Thereafter a series of papers appeared on the embryology of the species. The following authors gave accounts dealing with phases of its development: Metschnikoff (1869), Balfour (1881), Ludwig (1881), Apostolides (1882), Fewkes (1887), Carpenter (1887), Hamann (1889), Cuenot (1891), Russo (1891), MacBride (1892), and Dawydoff (1901).
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With the close of the nineteenth century research on the subject came to an end, leaving a series of accounts so conflicting not only with what was then known of other ophiuroids, but also with one another, that MacBride in 1914 made only a passing reference to the species in his “Text-book of Embryology.” He quotes, however, Ludwig's work on the development of the skeleton, and his own work on the late development of the ovoid gland and related structures; but as the findings of the previous workers, such as Apostolides (1882) and Russo (1891) differed widely from what had been found for Ophiothrix fragilis, he regarded their statements as “improbable in the highest degree.”
In order to bring out more clearly the questions most in dispute, it is preferable to give a comparative table of previous results under subject-headings, rather than a purely chronological list of workers and their findings. This is set out as follows:—