Youson J H, Ooi E C
Am J Anat. 1979 Jun;155(2):201-21. doi: 10.1002/aja.1001550205.
The renal corpuscle of the adult lamprey, Petromyzon marinus L., is formed during the programmed period of metamorphosis. Development is initiated early in this metamorphic period and is marked by the synchronous formation and growth of rudimentary nephron units (RNU) from longitudinal cord of nephrogenictissue extending from the posterior tip of the degenerating larval kidney to the cloaca and connected to the peritoneal epithelium. Detachment of the RNU from the peritoneum involves autolysis and cell death and is accompanied by their branching into five or six hexagonally-arranged nephrons which radiate from the original point of attachment. Differentiation of the epithelial cells at the proximal ends of the nephrons is preceded by the widening of lateral intercellular spaces, the formation of tubular lumina (primitive urinary spaces), the loss of apical cell junctions, and the development of a capillary network with its associated mesangium. With the extension of the capillaries and mesangium between the proximal ends of adjacent undifferentiated nephrons, visceral epithelial cells (podocytes), with long cell processes (trabeculae) and slit membranes, make their appearance. The urinary spaces resulting from this form of development are lined by the epithelium of the dilated ends of the nephrons (nephric capsules). The cells of these capsules differentiate mainly into podocytes, but a few parietal cells connect to the draining tubule. This method of development explains the unique form of the renal corpuscle in the adult lamprey. Despite the type of morphogenesis, this renal corpuscle possesses the fine-structural features seen in the renal corpuscles of other vertebrates.
成年海七鳃鳗（Petromyzon marinus L.）的肾小体是在变态的程序化时期形成的。发育在这个变态时期早期开始，其标志是从退化的幼体肾脏后尖端延伸至泄殖腔并与腹膜上皮相连的肾发生组织纵索同步形成和生长出初级肾单位（RNU）。RNU与腹膜分离涉及自溶和细胞死亡，并伴随着它们分支形成五六个呈六边形排列的肾单位，这些肾单位从原始附着点呈放射状分布。在肾单位近端的上皮细胞分化之前，细胞间侧间隙增宽，形成管状腔（原始尿腔），顶端细胞连接丧失，以及形成带有相关系膜的毛细血管网。随着毛细血管和系膜在相邻未分化肾单位近端之间延伸，出现了具有长细胞突起（小梁）和裂孔膜的脏层上皮细胞（足细胞）。这种发育形式产生的尿腔由肾单位扩张末端（肾小囊）的上皮细胞衬里。这些小囊的细胞主要分化为足细胞，但少数壁层细胞与引流小管相连。这种发育方式解释了成年海七鳃鳗肾小体的独特形态。尽管形态发生类型不同，但这种肾小体具有其他脊椎动物肾小体中所见的精细结构特征。
