On referring to my notes I find that the lemur had arrived in England about four months previously. [Illustration: FIG. 54.--_Cœnurus lemuris._ 1, Colony; 2, portion of the ectocyst (enlarged); 3, scolex-head (magnified 40 diameters); 4, hooks (magnified 260 diameters). Original.] Larval cestodes do not appear to be common in the monkeys of the New World (Cebidæ), nevertheless I found several Cysticerci in the liver of _Macacus radiatus_ (Feb. 19th 1857), and a single specimen in the sooty monkey (Dec. 4th 1857). They were wrongly described by me as Cercariæ. The Cebidæ are largely infested with tapeworms (_Tænia megastoma_ and _T. rugosa_). A species of Ligula (_L. reptans_) has likewise been found beneath the skin of _Callithrix sciureus_ and in one of the marmosets (_Hapale melanurus_). Perhaps the most common helminth infesting monkeys is the nematode called _Filaria gracilis_. I have examined specimens from the orang, the capuchin, and the spider monkey. This parasite commonly occupies the abdomen, coiled beneath the peritoneum, or within folds of the mesentery. It sometimes occurs beneath the skin, or within the connective tissue of superficial muscles. The female worm has been known to reach a length of five feet. In 1873 Mr Samuel Smith, of Clifton, sent me five specimens of this worm. From one of the males, which measured twenty inches in length, I procured some spermatozoa, and found their long diameter to average 1/1400″. These corpuscles and other structures, as well as the worm itself, are figured in my ‘Notes on Entozoa’ quoted below. Next in frequency, perhaps, is the whipworm (_Trichocephalus dispar_), which monkeys of all kinds harbor in common with man. Besides these nematodes, _Physaloptera dilatata_ is found in the stomach of American monkeys, and _Ascaris distans_ also (in the large intestine of marmosets more particularly). This Ascaris has also been found in _Cercopithecus fuliginosus_ and in _Simia sabæa_. A small spiroptera is said to infest the walls of the stomach of _Simia maimon_. To Dr Murie I am indebted for a large roundworm (_Ascaris lumbricoides_) taken from the intestine of a chimpanzee (_Troglodytes niger_), and also for a smaller nematode taken from a green mona-monkey (_Cercopithecus_). This I have described and named _Ascaris cuspidata_. From the intestines of a chacma (_Cynocephalus porcarius_) M. Schafhert procured sixteen examples of a small strongyle (_Str. attenuatus_, Leidy).