. Tetramicra brevifilum gen, n. sp, n. is described from the connective tissues throughout the body musculature of turbot Scophthalmus maximus (L.). Uninucleate spores (4.8·2 μm) are characterized by a large posterior vacuole, electron dense inclusion bodies in cytoplasm and nucleus and short filaments with 3–5 coils (50 μm extruded). Sporogony is apansporoblastic and tetrasporoblastic, within a host vacuole. Features of the xenoma (2 mm diameter) include a microvillous surface layer with microtubules and microfilaments and a reticulate nucleus with numerous nucleoli. Adherence between adjacent xenomas results in composite cysts of various sizes and shapes depending on site, being dendritic in the myomeres, arms extending between the fibres. Effects on the host, other than eventual destruction of the host cell, include displacement of muscle fibres in myomeres with loss of attachment to myocommata. Breakdown of the xenoma with release of spores into the connective tissue matrix was associated with a localized necrosis affecting surrounding muscle fibres, with leucocyte infiltration and collagen deposition. Spores phagocytosed by macrophages were destroyed in vacuoles, some with multi‐laminate walls. Experimental infections established by intramuscular injection at marked sites remained localized, which suggested that xenomas afford sufficient scope for spore production without the need of secondary invasion. The swimming efficiency of turbot would be impaired in severe infections leading to lowered growth rates and increased mortality in wild populations due to predation and starvation. Feeding hierarchies exist in turbot and the disease could prove significant in farming conditions.

progressive increases in both the glomerular filtration rate and the renal plasma flow during pregnancy, and that these changes reach a maximum in the third trimester and return to normal during the puerperium. This relationship appears to have been little studied except in man, and it therefore seemed worth while to find out whether similar changes occur in animals. Some of the results have already been published in a preliminary communication (Matthews & Taylor, 1959). METHODS Animals and diet. Virgin hooded rats of the Rowett strain, 3-4 months old and weighing between 200 and 300 g, were fed on the stock diet described by Thomson (1936), but differing from it in a higher content of skim milk (14 % instead of 7 %).Mating. Male and female rats were placed together for a period of 16 hr, and the duration of pregnancy was timed from the day of mating.Operative procedure. The method of Pritchard & Huggett (1947) was used for the removal of foetuses while leaving the placentas in situ, with the modification that the foetuses were removed from both uterine horns through a mid-line abdominal incision.Anaesthesia. Pentobarbitone sodium B.P. (Veterinary Nembutal; Abbott Laboratories Ltd.; 5-5 mg/100 g body wt.) was given by intraperitoneal injection.Determination of plsma inulin and para-aminohippurate (PAH) clearances. All methods used for collecting blood and urine from small animals have presented numerous difficulties (Smith, 1951) but despite this the results of many methods agree well. Dicker (1956) has pointed out that provided the urine collections are made while the concentration of inulin or PAH is changing quite slowly, the single subcutaneous injection technique will yield reasonably accurate results.Inulin was supplied by Messrs Kerfoot and Co. Ltd., and the PAH obtained from L. Light and Co. Ltd. Two solutions, the pH of which was adjusted to approximately 7 0, were prepared for injection. One consisted of inulin 5 g/100 ml. and mannitol 5 g/100 ml. in 0-9 % (w/v) NaCl solution. The other consisted of PAH 1-25 g/100 ml. in 0-9% (w/v) NaCl solution. Of inulin-mannitol solution, 1 ml./100 g body weight was injected. The amount of PAH solution to be injected was estimated from Friedman's dosage curve (Friedman, 1952) and varied between 4 0 and 4-5 ml. Ten minutes after the administration

Cryptocaryon irritans was isolated from Grammistes sexlineatus and maintained in aquaria under controlled conditions using the mullet. Chelon labrosus (Risso), as an experimental host. The pellicle and eortieal eytoplasm of the trophont, tomont. tomite and thcront stages were investigated with the aid of transmission electron mieroseopy. The general structural organization of the pellicle resembles that of the freshwater holotrieh, Ichthyophthirius multifiliis: however, the peDieular alveoli are charaeterized by the aeeumulation of electron-dense material in the trophont, tomite and theront, this material being lost in the newly-encysted tomont. The outer membranes of the pellicle are infolded into the alveoli of the trophont. Cilia are present at all stages of the life cycle, although at encystment their numbers are greatly reduced by shedding. Mitochondria, mucoeysts and Golgi-like cisternae are distributed throughout the cortical cytoplasm. Mucoeysts differ from those of /. miiltifiliis in size, shape and distribution and arc of uniform electron density. The role of the pellicle and cortical cytoplasm is discussed in relation to the invasion of the fish epidermis, possible intcrtransteranee of materials between parasite and host and the process of encystment.

SUMMARYCercaria vaullegeardi develops in daughter sporocysts within the digestive gland of the prosobranch Gibbula umbilicalis. On emergence into the host mantle cavity the cercarial body retracts into the cystophorous tail, the ‘encysted’ cercaria being then shed into the sea. The encysted cercaria is described at the ultrastructural level for the first time and developmental stages are redescribed. The cercarial body has no penetration or cystogenous glands: a single type of sub-tegumental secretory cell produces vesicles containing neutral mucopolysaccharides which pass into the tegument at encystment. The immotile cystophorous tail consists essentially of a fibrous caudal cyst and 8 appendages including a delivery tube. Scanning electron micrographs show the surface of tegumental membranes enveloping the caudal cyst to be covered with a honeycomb pattern of indentations derived from electron-lucent vesicles produced by the caudal gland. The fibrous-walled delivery tube comprises proximal and distal sections and a modified terminal end-piece.

The teleost stomach, as a site of strong acid proteolytic digestion at pH 1–4, is a hostile environment rarely chosen as a habitat by parasites. Several Hemiuroidea have nevertheless invaded this niche, notably the Hemiuridae, a family in which the body is characterized by a retractile “tail”, or ecsoma. The structure and function of the latter has been studied in three hemiurid species, namely Hemiurus communis, Lecithochirium rufoviride and L. fusiforme, using ultrastructural, histochemical and autoradiographic techniques. Results indicate a clear demarcation between the function of the tegument covering the ecsoma and that of the rest of the body, or soma. No mitochondria have been observed in the ecsomal tegument, and intense acid phosphatase activity was detected in association with its outer plasma membrane. Uptake of 3H-tyrosine occurred within the excretory vesicle, which may serve for transport of nutrients forwards into the soma. In contrast, the thickened, dense somal tegument, with few mitochondria largely confined to ridges or plications in H. communis, showed neither phosphatase activity nor uptake of tyrosine. Glucose uptake was not detected in any part of the body. That the somal tegument serves not for absorption but for protection against both physico-chemical conditions and mechanical damage by prey entering the host's stomach is discussed.