Platel R, Vesselkin N P
Université Paris 7, Laboratoire d'Anatomie comparée 2, France.
J Hirnforsch. 1989;30(1):23-32.
This study has been carried out upon 3 species of Petromyzonts: Petromyzon marinus, Lampetra fluviatilis and Lampetra planeri. According to the values of the index of encephalization (whole brain) and to these of the structures indices (brain subdivisions), similarities as well as differences have been pointed out. Other detail are brought by the relative volume of these subdivisions expressed by a per cent value of the entire brain volume (the ventricular volumes being removed). 1. The indices of encephalization show that the Sea Lamprey is the less encephalized species amongst Vertebrates (with an arbitrary value of 10); but the 2 other lampreys stay at a higher level (respectively 44 and 38) while the Hagfish reaches 54 and the average encephalization index of bony fishes locates at the 100 value. 2. The relative volumes lead to a quantified brain pattern which characterizes the both 3 Lampreys with regard to the other species of Vertebrates: olfactory bulbs are well developed, more than the cerebral hemispheres; at the same time the so-called structure Tegmentum + Medulla oblongata holds about 50% of the entire brain volume. This dual pecularity may be considered as the expression of a primitive status. 3. The structure indices (each of it being fixed at 10 for the Sea Lamprey) are uniformly higher in the 2 Lampetra (with a step of 20 to 30 unities of index). It seems to be, this time, the expression of an inner evolution in Petromyzonts, but remaining the basic pattern of the group. Some examples taken amongst other Vertebrates emphasize this pecularity: Polypterus possess high indices for the cerebral hemispheres (595: processus of telencephalization) and cerebellum (1250). On the other hand the Sturgeon shows low values for all the subdivisions, except cerebellum (549). Finally, the Hagfish withdraws from the brain pattern of Lamprey because its indices are clearly higher for olfactory lobes (141) and diencephalon (113).
本研究对3种七鳃鳗进行了观察，分别是海七鳃鳗（Petromyzon marinus）、河七鳃鳗（Lampetra fluviatilis）和平额七鳃鳗（Lampetra planeri）。根据脑化指数（全脑）值以及各结构指数（脑部分区）值，指出了它们之间的异同。通过以全脑体积的百分比值（去除脑室体积）表示的这些分区的相对体积，还得出了其他细节。1. 脑化指数表明，海七鳃鳗是脊椎动物中脑化程度最低的物种（任意值为10）；但另外两种七鳃鳗处于较高水平（分别为44和38），而盲鳗达到54，硬骨鱼的平均脑化指数为100。2. 相对体积导致了一种量化的脑模式，该模式在3种七鳃鳗与其他脊椎动物物种之间具有特征性：嗅球发育良好，比大脑半球更发达；同时，所谓的被盖 + 延髓结构占整个脑体积的约50%。这种双重特性可被视为原始状态的一种表现。3. 结构指数（海七鳃鳗的每个指数固定为10）在另外两种七鳃鳗中均较高（指数步长为20至30个单位）。这似乎是七鳃鳗内部进化的一种表现，但仍保留了该类群的基本模式。从其他脊椎动物中选取的一些例子强调了这种特性：多鳍鱼的大脑半球（595：端脑化过程）和小脑（1250）指数较高。另一方面，鲟鱼除小脑外（549），所有分区的值都较低。最后，盲鳗与七鳃鳗的脑模式不同，因为其嗅叶（141）和间脑（113）的指数明显更高。
