By using stereoscopic microscope and SEM,15 coloured replica casts of the bi-liary tract and hepatic arterial system in the liver of the guinea pigs were investi-gated.The liver of the guinea pig has 6 lobes.There are one bile duct and one hepaticartery which enter each lobe through its porta.In each lobe,both the bile duct andthe hepatic artery are divided repeatedly 6 to 10 times according to the size andshape of the lobe.These branches may be called the main branches.The averagedivergent angle of the main branches is 52.4??13.05(N=158).There are alsomany very small branches which arise from the main branches of all grades.Theoriginating angle of most side branches is about 90?.After investigating 110 peribiliary vessel plexuses of the guinea pigs,we foundthat they are of two different types:When the diameter of the bile duct is morethan 95～100 ?m,its peribiliary vessel plexus consists mainly of capillaries which arearranged as a reticulate sheath.When the diameter of the bile duct is less than 95～100 ?m,its peribiliary vessel plexus consists mainly of arterioles which appears asa longitudinal vessel plexus.From the origin and course of the longitudinal ves-sels,we can presume that the direction of the blood flow in the vessels is opposite tothat of the bile flow in the bile duct surrounded by the longitudinal vessels.Thelength of the longitudinal vessel plexuses is about 2,000～4,000 ?m.

The blood vascular casts of the small intestine of sevcral laboratory animals (15 guinea pigs, 5 mice, 3 rats, 2 rabbits and 1 monkey) have been investigated in stereo-microscope and scanning electron microscope. We pay particularly attention to the architecture of the villous blood vascular plexus.According to the characteristics of the structure, the villous blood vascular plexus of guinea pig, mouse, rabbit, and monley may be described as "the tuft pattern"; while that of rat as "the fountain pattern". However, there are some obvious differences between all of them.In guinea pig, rabbit and monkey, there are recti blood vessels at the lower part of the villus. They assume the characteristics of portal vessels in guinea pig and rabbit.The significance of the different patterns and the presence of recti vessels in the villous blood vascular plexus of the small intestine were discussed.

The renomedullary interstitial cells (RMIC) of rat were investigated using the method of HCl-Tween removing extracellular material and scanning electron microscope. According to the shape and distribution, the RMIC may be divided into 3 groups. However, most of RMIC belong to the first group.The cell of the first group is fibroblast-like, which has an irregular cylindrical body (about 2-6 ?m in short diameter and 5-12 ?m in long diameter) and several processes from both ends of the body. The processes from one end are distributed on the wall of the renal tubule (Henle's loop or collecting tubule); and those from the other end on the blood vessel, sometimes, with the vascular pedicles formed by the expanding of the process end. The long axis of the cells of the first group is perpendicular to the tubules and blood vessels, so the cells are bridged between them.The second group cell has a round body without process and is located at the body of the first group cell.The third group cell is star-like, which has a large body (about 5-8 ?m in diameter) and a few small processes. They are randomly distributed, and sometimes, arranged as a line along the blood vessel.

By using replica cast SEM method, the vascular architecture of the dental pulp of rat incisors was studied. The characteristics of the vascular architecture are as follows:1. The axis of the dental pulp is occupied by the central vascular bundle, which consists of 10 to 20 arterioles and 8 to 12 venules.2. The arterioles (30-50?m in diameter) and the venules (50-80?m in diameter) located in the central bundles are arranged parallely in a relatively long distance as a countercurrent system. The longest distance is about 12 mm.3. Each arteriole of the central vascular bundle supplies an independent area of the dentin of the tooth. The territory of an arteriole is about 700 to 1400 ?m in length.4. The arteriole of the central bundle breaks up into capillaries (4～6?m in diameter) which are mainly distributed over the odontblast area and form a complex 3-dimensional plexus.

The microvascutature of the adrenal medulla in the rats and mice were studied by scanning electron microscopy of vascular replicas.There are portal venules between the adrenal cortex and medulla,which are the side branches of the collecting venules of the adrenal cortex and break into capillaries at the adrenal medulla.The adrenal medulla in mice is mainly supplied by these portal venules,and in a rat adrenal medulla,there are also 5—8 medullar arterioles besides the portal venules.Ring-like constrictions appear to be the characters of sphincter at the ending parts of the portal venules,the branches of the medullar arterioles,the collecting venules,and the medullar venules which drain the medullar capillaries as well.The authors believe that the adrenal cortex controls the medulla by the way of the portal venules.

The microvasculature of the submandibular glands of guinea pig's was studied with the replica-SEM msthod. Special attention was paid to the microvascular architecture around the glandular ductal tree, which is mainly dichotomous, but usually asymmetrical and irregular, with a divergent angle of 40-80? and 7-8 grades of branching. The ductal tree is surrounded with a periductal vascular plexus. The periductal plexus of the excretory ducts can be divided into two layers: the inner layer is formed by capillaries and the outer layer by veins, so called venous coat. This venous coat is complexly constructed with button veins, loop veins and complicated venous circulatory by-passes. The capillary plexus of the striated ducts and intercalated ducts is supplied by venules with the cha-ractristics of the portal vein as they come from the capillaries of the acini. There are complex A-V and V-V anastomoses at the venous coat and at the lobu-lar porta.The significance of the microstructures described above was discussed.

The microvasculature of the lung of three humans was studied with the replicascanning electron microscopic method. The pulmonary arteriole belongs to microvasculature at the level of the respiratory bronchiole and gives out some side branches to the alveoli. The diameter of the arteriole is about 30-50 ?m. The arteriole divided into terminal arterioles, which accompanied with primary alveolar ducts. The diameter of the terminal arteriole is about 10-20 ?m, 17.35?1.62 ?m in average (n=30). There are obvious imprints of smooth muscles and endothelial nuclei on the surface of the casts of arteriole and terminal arteriole. The diameter of the alveolar capillary is 5.87?0.90 ?m in average (n=500). The proportion of the capillary area arround the alveole is 66?1.4%. There are two patterns of capillary network, i. e. long mesh and round mesh in type. The diameter of the mesh is (9.24?2.02)?(5.65?1.40) and 5.75?0.84 ?m, respectively. The distance of the mesh center is 17.13?1.74 ?m (long) and 11.52?1.12 ?m (short) in long mesh, and 11.63?0.88 ?m in round mesh. The capillary network of the long mesh located at the entrance and the base of the alveoli; and the round mesh in the area between them. The metaarteriole supplying the alveoli enters the alveoli at their entrance and thev venule draining the alveoli at their base. The distance between them is about 330 ?m.According to the microvascular architecture, the pulmonary microvasculature may be divided into three ordered units: i. e. the alveolar, the alveolar duct, and the respiratory bronchiolar units.