I would wish to lay particular stress upon the composition of this (the stomach) and other organs of the Medusae out of TWO DISTINCT MEMBRANES, as I believe that it is one of the essential peculiarities of their structure, and that a knowledge of the fact is of great importance in investigating their homologies. I will call these two membranes as such, and independently of any modifications into particular organs, "foundation membranes." [And in section 56 (page 23) one of the general conclusions which he deduces from his observations, is] That a Medusa consists essentially of two membranes enclosing a variously-shaped cavity, inasmuch as its various organs are so composed, [a peculiarity shared by certain other families of zoophytes. This is a point which that eminent authority, Professor G.J. Allman, had in his mind when he wrote to call my attention "to a fact which has been overlooked in all the notices I have seen, and which I regard as one of the greatest claims of his splendid work on the recognition of zoologists. I refer to his discovery that the body of the Medusae is essentially composed of two membranes, an outer and an inner, and his recognition of these as the homologues of the two primary germinal leaflets in the vertebrate embryo. Now this discovery stands at the very basis of a philosophic zoology, and of a true conception of the affinities of animals. It is the ground on which Haeckel has founded his famous Gastraea Theory, and without it Kowalesky could never have announced his great discovery of the affinity of the Ascidians and Vertebrates, by which zoologists had been startled."] CHAPTER 1.4. 1848-1850. [The whole cruise of the "Rattlesnake" lasted almost precisely four years, her stay in Australian waters nearly three. Of this time altogether eleven months were spent at Sydney, namely, July 16 to October 11, 1847; January 14 to February 2, and March 9 to April 29, 1848; January 24 to May 8, 1849; and February 14 to May 2, 1850. The three months of the first northern cruise were spent in the survey of the Inshore Passage--the passage, that is, within the Great Barrier Reef for ships proceeding from India to Sydney. In 1848, while waiting for the right season to visit Torres Straits, a short cruise was made in February and March, to inspect the lighthouses in Bass' Straits. It was on this occasion that Huxley visited Melbourne, then an insignificant town, before the discovery of gold had brought a rush of immigrants.