Wilkinson J M, Coggeshall R E
J Comp Neurol. 1976 Dec 1;170(3):381-9. doi: 10.1002/cne.901700308.
The central nervous system of Hirudo medicinalis is contained within a blood vessel, the ventral longitudinal sinus, but the nervous system is separated from the blood by the visceral endothelium. The visceral endothelium possesses many pinocytotic vesicles and basal infoldings and thus appears active whereas the parietal endothelium appears inactive. The junction between the visceral and parietal endothelia is abrupt. Peripheral nerves in this animal, as in vertebrates, are covered by endoneurium, perineurium, and epineurium. The endoneurium is continous with the fibrous tissue of the segmental ganglia. The perineurium, consisting of a single layer of flattened cells that surrounds the peripheral nerve like a sleeve, is not continuous with the endothelium of the ventral sinus, but is separated from it by 5-10 microns. Therefore, at the point where the peripheral nerve joins the segmental ganglion, the extracellular spaces of the central nervous system, the peripheral nervous system, and the body wall are all confluent. Thus, there are only two compartments of the extracellular space in the leech: the blood, which is enclosed by the endothelia of the coelomic sinuses, and the extracellular fluid of the body, which includes the extracellular fluid of the nervous system. There seems to be no equivalent of cerebrospinal fluid in the gnathobdellid leech.
医蛭的中枢神经系统包含在一条血管——腹侧纵窦内，但神经系统通过内脏内皮与血液分隔开。内脏内皮有许多胞饮小泡和基底褶皱，因此显得活跃，而体壁内皮则显得不活跃。内脏内皮和体壁内皮之间的连接是突然的。与脊椎动物一样，这种动物的外周神经被神经内膜、神经束膜和神经外膜覆盖。神经内膜与节段神经节的纤维组织相连。神经束膜由单层扁平细胞组成，像袖子一样围绕着外周神经，它与腹侧窦的内皮不连续，而是与之相隔5 - 10微米。因此，在外周神经与节段神经节相连的部位，中枢神经系统、外周神经系统和体壁的细胞外间隙都是相通的。因此，水蛭的细胞外间隙只有两个隔室：被体腔窦内皮包围的血液，以及身体的细胞外液，其中包括神经系统的细胞外液。颚蛭目水蛭似乎没有相当于脑脊液的物质。
