In the museum of the Royal Veterinary College there are a number of excellent preparations of true hydatids taken from various animals, especially from cattle, swine, and sheep; and there are also many kinds of bladder worms which, though often called “hydatid” by veterinarians, have a totally different origin from that of the true Echinococci. The so-called gid-hydatids (Cœnuri) and slender-necked hydatids (_Cysticercus tenuicollis_) are of this description. Specimens of the polycephalous brain hydatid, or Cœnurus, also exist in the museums connected with St Bartholomew’s, Guy’s, and St Thomas’s Hospital Medical Colleges, as well as in both the anatomical and pathological departments of the Oxford Museum. Specimens of large Cœnuri occurring in the soft parts of rabbits may be seen in the Guy’s Museum (presented by Mr Carpenter). Similar characteristic specimens exist in the Oxford Collection, labelled _C. cuniculi_, obtained from the “masseter and infraspinatus” muscles of a rabbit. My private collection also contains a recent addition of this remarkable hydatid, sent to me by Mr Alston from Ayrshire. It is the only one I have seen from Scotland. In the second half of this work these Cœnuri will again come under notice. Three examples of the slender-necked hydatid (from a monkey and two sheep respectively) may be seen in the Guy’s and University College Collections, and there are several in the museum of the Royal Veterinary College. I cannot go out of my way to speak of other bladder worms, except so far as to call attention to the heart of a bear preserved in the museum at Guy’s, the walls of which are crowded with Cysticerci. That unique preparation ought to be carefully examined and described. The Hunterian Museum contains two magnificent specimens of hydatids affecting the bones of cattle. In the one case a solitary vesicle occupies the shaft of the humerus; whilst in the other several “acephalocysts” have taken up their residence within the cancellous structure of the ilium. In the matter of human mortality from hydatids I have already supplied statistical evidence of the unenviable distinction which our Australian colonies exhibit, and in addition to the facts brought forward I may add that Dr Lewellin has mentioned to me a fatal case in which an hydatid occupied the whole length of the vertebral canal. The patient was under Dr Annand’s care. There could be no doubt as to the genuineness of the case, as the spinal cyst was tapped during life, when echinococcus hooklets were found. Through Dr Lewellin I am also indebted to Dr H. B. Allen, pathologist at the Melbourne Hospital, for the particulars of a case of hydatids of the cerebrum, which are given as follows: “J. Q--, aged 15, was admitted into the Melbourne Hospital on the 13th November, 1877, suffering from partial left hemiplegia. He rapidly became insensible and died next day. His mother furnished the following history.