5. Upon Pyrosoma and Salpa. The former has never been described (I think) since Savigny's time, and he had only specimens preserved in spirits. I have a great deal to add and alter. Then as to Salpa, whose mode of generation has always been so great a bone of contention, I have a long series of observations and drawings which I have verified over and over again, and which, if correct, must give rise to quite a new view of the matter. I may mention as an interesting fact that in these animals so low in the scale I have found a PLACENTAL CIRCULATION, rudimentary indeed, but nevertheless a perfect model on a small scale of that which takes place in the mammalia. 6. I have the materials for a monograph upon the Acalephae and Hydrostatic Acalephae. I have examined very carefully more than forty genera of these animals--many of them very rare, and some quite new. But I paid comparatively little attention to the collection of new species, caring rather to come to some clear and definite idea as to the structure of those which had indeed been long known, but very little understood. Unfortunately for science, but fortunately for me, this method appears to have been somewhat novel with observers of these animals, and consequently everywhere new and remarkable facts were to be had for the picking up. It is not to be supposed that one could occupy one's self with the animals for so long without coming to some conclusion as to their systematic place, however subsidiary to observation such considerations must always be regarded, and it seems to me (although on such matters I can of course only speak with the greatest hesitation) that just as the more minute and careful observations made upon the old "Vermes" of Linnaeus necessitated the breaking up of that class into several very distinct classes, so more careful investigation requires the breaking up of Cuvier's "Radiata" (which succeeded the "Vermes" as a sort of zoological lumber-room) into several very distinct and well-defined new classes, of which the Acalephae, Hydrostatic Acalephae, actinoid and hydroid polypes, will form one. But I fear that I am trespassing beyond the limits of a letter. I have only wished to state what I have done in order that you may judge concerning the propriety or impropriety of what I propose to do. And I trust that you will not think that I am presuming too much upon your kindness if I take the liberty of thus asking your advice about my own affairs. In truth, I feel in a manner responsible to you for the use of the appointment you procured for me; and furthermore, Captain Stanley's unfortunate decease has left the interests of the ship in general and my own in particular without a representative.