In addition to acting as channels for the conveyance of bacterial infection, _lymph vessels frequently convey the cells of malignant tumours_, and especially cancer, from the seat of the primary disease to the nearest lymph glands, and they may themselves become the seat of cancerous growth forming nodular cords. The permeation of cancer by way of the lymphatics, described by Sampson Handley, has already been referred to. #Lymphangiectasis# is a dilated or varicose condition of lymph vessels. It is met with as a congenital affection in the tongue and lips, or it may be acquired as the result of any condition which is attended with extensive obliteration or blocking of the main lymph trunks. An interesting type of lymphangiectasis is that which results from the presence of the _filaria Bancrofti_ in the vessels, and is observed chiefly in the groin, spermatic cord, and scrotum of persons who have lived in the tropics. _Filarial disease in the lymphatics of the groin_ appears as a soft, doughy swelling, varying in size from a walnut to a cocoa-nut; it may partly disappear on pressure and when the patient lies down. The patient gives a history of feverish attacks of the nature of lymphangitis during which the swelling becomes painful and tender. These attacks may show a remarkable periodicity, and each may be followed by an increase in the size of the swelling, which may extend along the inguinal canal into the abdomen, or down the spermatic cord into the scrotum. On dissection, the swelling is found to be made up of dilated, tortuous, and thickened lymph vessels in which the parent worm is sometimes found, and of greatly enlarged lymph glands which have undergone fibrosis, with giant-cell formation and eosinophile aggregations. The fluid in the dilated vessels is either clear or turbid, in the latter case resembling chyle. The affection is frequently bilateral, and may be associated with lymph scrotum, with elephantiasis, and with chyluria. The _diagnosis_ is to be made from such other swellings in the groin as hernia, lipoma, or cystic pouching of the great saphenous vein. It is confirmed by finding the recently dead or dying worms in the inflamed lymph glands. _Treatment._--When the disease is limited to the groin or scrotum, excision may bring about a permanent cure, but it may result in the formation of lymphatic sinuses and only afford temporary relief.