In the museum at University College, I examined sixteen preparations of hydatid disease, representing almost as many distinct cases. One is a wax model. Eight of the specimens were from the liver, five from the abdomen (including those of the omentum and mesentery), two from the lungs, and one from the heart. The model displayed ordinary hydatids of the liver bursting into the lungs. The mesenteric example is particularly fine, whilst that from the omentum is undergoing calcareous degeneration. Probably the most interesting of all is the example showing an hydatid lodged in the septum of the heart. This was from a middle-aged female, who died suddenly whilst pursuing her ordinary domestic avocations. The museum of the Royal College of Surgeons contains a fine collection of parasites, its chief strength in this respect being due to the special series of entozoa. Were visitors to judge by the contents of the catalogue of this series (which I prepared some years ago at the instance of the Council of the College), they might be led to suppose that the hydatids were only feebly represented. Out of nine preparations of hydatids in this section, only six have come from the human body. However, scattered throughout the collection, I found that there were no fewer than thirty-five preparations of hydatids belonging, apparently, to as many as thirty separate cases. Omitting, for the present, all mention of these derived from animals, I ascertained that, of the thirty human cases, thirteen were referable to the liver, four to the abdomen, three to the lungs (one of which was originally connected with the liver), and two to the brain. Five were of uncertain seat. With the abdominal cases we may also include one case of hydatids of the spleen, and another where these organisms were found in the region of the bladder. There is a characteristic breast case. One of the original Hunterian cases (in which “a prodigious number of hydatids were found in the sac of the liver and dispersed throughout the cavity of the abdomen”) appears, though it is not expressly so stated in the catalogue, to have been regarded as an ordinary example of abdominal dropsy. In one of the three lung cases two small hydatids were separately expectorated at an interval of about a month. This occurred in a female. I may here incidentally remark that many cases are on record where abdominal hydatids have been overlooked, the patient being supposed to be suffering from ascites. One such instance took place a few years ago at the Middlesex Hospital. I well remember a similar case of supposed hydrothorax, where the post-mortem examination revealed the presence of immense numbers of these formations occupying the right side of the chest. This case occurred at the Norfolk and Norwich Hospital, at the time when I was a student there, some thirty-five years ago.