Peer review is usually a labor of love. Even on a good day, reconsider after major revision is the most common recommendation, and an unblinking accept a rarity. Occasionally a reviewer is privileged to read an absolute jewel of a paper and writes an opening sentence that begins “The manuscript by Norifumi Konno et al. is a pleasure to read, and the following comments are counsels of perfection rather than criticisms.” The paper documents the endocrinology of water homeostasis in the African lungfish. Lungfish are extraordinary creatures,withlungsandgills, livingrecordsoftheevolutionary transition from aquatic to terrestrial life. Today they are most commonly found in high-end pet shops, but their free-living condition in the old Gondwanaland radiation is in the seasonal streams and swamps in Africa, South America, and Australia. Konno et al. (1) have characterized the vasotocin (VT)/aquaporin (AQP) axis in lungfish, parallel to the mammalian vasopressin/AQP AQP2 axis, and establish how lungfish cope when the seasonal streams and marshes dry up each year. When “sumer is icumen in” (2) the lungfish estivates, and water conservation becomes a survival issue. In the free-living state, they do this by immuring themselves in a cocoon of mucus and mud; in the laboratory, Konno et al. (1) induced estivation by isolating each one in a approximately 4-liter plastic bag (think cask wine), with a bed of damp cotton and at 80% humidity. Within a week, each lungfish had encased itself in a brown dried mucus cocoon. After 90 d of induced estivation, the lungfish (hereafter EST) were removed and studied immediately or after 4, 8, and 24 h reacclimation to fresh water. All groups were then compared with animals maintained over the 90 d in fresh water (hereafter the FW group). Some of the changes in the EST group are not surprising. Mean body weight decreased by 16%, plasma [Na ] rose 22%, plasma osmolality 59%, and plasma urea 30fold (as shown in Table 1 in the paper, rather than the 13.1-fold noted in the text). The variance around mean values for osmolality is 10-fold higher in EST than in FW, whereas the variance for plasma urea is the same (as a percentage of the mean) for the two groups. Given the extent of the change in plasma urea, it is difficult to question the authors’ assertion that “An increased plasma urea appears to be a major factor for the hyperosmolality caused under estivation;” it would be interesting, however, to see a plot of individual values, urea vs. osmolality. The study is linear and measured: first, the molecular and evolutionary characterization of AQP in the lungfish kidney; then, the demonstration of its crucial role in EST. Using degenerate primers based on tetrapod AQP2 sequences, theauthorsclonedtwolungfishAQPs,onefromthe eye (lfAQPO) and the other from the kidney, termed lfAQPOp, i.e. a paralogue of lfAQPO. Molecular phylogeneticanalyses showedthat thekidney formsharesacommon immediateancestorwithAQPOafterthebranchingoffofthe AQP2 subfamily. It should come as no surprise that AQPOp has been pressed into service in an AQP2-like role: for example, prolactin has well-characterized mammalian actions, but in newts is responsible for eft water drive. Functional characterization of lfAQPOp then methodically followed. Xenopus oocytes were injected with lfAQPOp cRNA, and 3 d later hypoosmotically challenged. Within 30 sec, cRNA injected oocytes began to swell, a process that increased linearly over the 3 min of observation and wasaugmentedbycAMP.Attheendofthestudy, theoocytes were fixed, and the presence of lfAQPOp demonstrated by immunocytochemistry. In terms of tissue distribution, the vasopressin/VT type 2 receptor is widely expressed (heart, kidney, brain, eye, gill, lung, testis, muscle, and skin). In EST, lfAQPOp was expressed at high levels in the kidney, and also in lung and gall bladder; in FW, it was expressed only in lung