. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NERVOUS SYSTEM OK PELAGIC NEMERTEANS. 127 divided into two or more lobes (Figs. 3, 4). The nerve itself lies external to the circular muscular layer, while the ganglia are internal to these muscles and interposed between the bundles of longitudinal muscles. The broad connection between ganglion and nerve therefore requires the penetration of the thin circular musculature. This is accomplished by the mere separation of ad- jacent circular fibers so as to leave a narrow slit through which the connection passes. ^-mmim. FIG. 4.
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NERVOUS SYSTEM OK PELAGIC NEMERTEANS. 127 divided into two or more lobes (Figs. 3, 4). The nerve itself lies external to the circular muscular layer, while the ganglia are internal to these muscles and interposed between the bundles of longitudinal muscles. The broad connection between ganglion and nerve therefore requires the penetration of the thin circular musculature. This is accomplished by the mere separation of ad- jacent circular fibers so as to leave a narrow slit through which the connection passes. ^-mmim. FIG. 4. Transverse sections of six of the ganglia of the dorsal nerve of Neuroncmcrtes aurantiaca Coa, showing variations in shape and their relations to the nerve core. A, Dorsal nerve between two adjacent ganglia. B, Small ganglion closely fused with dorsal nerve. C, Large ganglion with ventral group of nerve cells. D, Surface view of ganglion, its con- nection with dorsal nerve being in an adjacent section. E, Large ganglion with three lobes of nerve cells and distinct intermuscular plexus. F', Large ganglion with four lobes of nerve cells ;imp, intermuscular plexus; other lettering as in Fig. 2. The cells composing the ganglia are similar in size and appear- ance to those which accompany the lateral nerve cords, and the cell boundaries are likewise rarely to be distinguished (Fig. 4). It has been difficult to determine the precise nature of these organs. That their component cells are the source of fibers which inner- vate the integument and musculatures seems highly probable. And it is also presumable that they supplement the nerve cells found in all species accompanying the lateral nerve cords, but there is no evidence that these latter cells are less abundant in this species than in other pelagic forms. A suggestion that may have some degree of plausibility is that they are associated with the great development of the dorsoventral musculature, particu- larly in the region where
Size: 2526px × 989px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
