. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 150 P. J. H. HARRISON AND D. C. SANDEMAN. OpN circuruesophageal \ connective Posterior Figure 5. Schematic drawing of the neuropils and fiber tracts in the cyprid brain, showing further possible subdivision. The protocerebrum includes the paired optic lobe neuropils (OLN), median protocerebral neuropils (MPN), and an unpaired dorsofrontal neuropil (DFN). Optic lobe neuropils receive input from compound eyes (CE) via the optic nerve (OpN). and from frontal filaments (FF) vi'i; the frontal filament tract (FFT). The small dorso
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 150 P. J. H. HARRISON AND D. C. SANDEMAN. OpN circuruesophageal \ connective Posterior Figure 5. Schematic drawing of the neuropils and fiber tracts in the cyprid brain, showing further possible subdivision. The protocerebrum includes the paired optic lobe neuropils (OLN), median protocerebral neuropils (MPN), and an unpaired dorsofrontal neuropil (DFN). Optic lobe neuropils receive input from compound eyes (CE) via the optic nerve (OpN). and from frontal filaments (FF) vi'i; the frontal filament tract (FFT). The small dorsofrontal neuropil (DFN) lies anterior to the PC and receives input via the median eye (ME). Median protocerebral neuropils are not directly linked to peripheral sense organs, but the lateral lobes are con- nected by the protocerebral commissure (PC). The deutocerebrum includes paired circular and median deutocerebral neuropils (CDN, MDN, respec- tively). Peripheral nerves from the deutocerebrum form the antennular nerve (AnN), and lateral lobes of the median deutocerebral neuropil are connected by the deutocerebral commissure (DC). Longitudinal fiber tracts extend from the posterior of both the MPN and MDN and contribute to the circumesophageal connectives. (Fig. 9B). Narrow "cilia-type" dendritic profiles ( ju,m in diameter), which can be identified by a 9 X 2 + 2 microtubule arrangement, are also present (Fig. 9C). The larger processes can be traced as far as the distal portion of this segment, whereas the outer dendritic segments of smaller cilia-type processes extend into each of the four short subterminal setae (Fig. 9C). Approximately 50 /um from the brain, the antennular nerve is associated with a cluster of neurons, which we refer to as the antennular soma cluster (Fig. 10). This group of cells was referred to as the antennular "ganglion" by Walley (1969), who proposed that the somatu were those of motor- neurons that had migrated out from the
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