On the Systematic Position of the Brachiopoda (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1873 Excerpt: ...In Aphrodite and Polynoe, according to Grube, there are more ventral ganglia than segments. It was at one time believed to be typical of the Articulata that each segment was characterized by a ganglionic enlargement of the ventral cord, and it was supposed to be particularly so with the higher Annelids. Claparede calls attention to the fact that this is not so in all cases, and especially in relation to the cephalic and thoracic ganglia. In the Nemerteans the ventral cord is widely separated, and runs along each side of the body, and without ganglionic enlargements. There appears to be, therefore, various conditions of the nervous system, in which there is in some a simple oesophageal collar; in others, a ventral nerve cord, which may be single, or divided into two lateral halves, sometimes widely separated, sometimes nearly approximating, with, or without, ganglionic enlargements or threads connecting them. In some worms accessory pedal ganglia are found. In the Brachiopoda we have two lateral ventral cords, widely separated, and connected at the oesophagus by ganglionic enlargements, which send off threads to the pallial membranes, and to the various muscles. In Lingula these lateral threads seem to be double, connected by commissures. In Discina, whose nervous system I have more especally studied, the nerve cords are bilaterally symmetrical, and widely divaricating. There are no ganglionic enlargements during their course to the posterior end of the body, but in their track sending off delicate threads, which in Lingula blend with their muscular fibres, or pass round the muscles blending with their exterior fibres. In Discina these lateral nerve cords terminate by ganglionic enlargements in the last two posterior muscles. These nerve cords were correctly...