Fig. 1. Diagram of the ganglia of _Nucula castrensis_, reconstructed from serial sections. The probable position of the connectives is shown and the proportionate distances between ganglia are given. The upper ganglion is the cerebro-pleural with large nerves leading off from the ganglion which is itself lobed into four chief lobes. The pedal ganglion is next. In section the pedal ganglion at one place seems to be made up of four parts which may correspond to four connectives from the cerebro-pleural although only one pair of connectives was clearly determined. The visceral ganglion is connected with the pedal below. ×70. Fig. 2. Cross section of cerebro-pleural ganglion. On the right side one of the lateral ganglia is shown. The one of the other side does not show because the section is not straight across. The dorsal side is up. ×300. Fig. 3. Section of the pedal mass of _Nucula_, through the center. The dorsal side is up. ×300. Fig. 4. Left side of the visceral mass of _Nucula_. Dorsal side up. ×300. Fig. 5. Nerve cells from the central nervous system of _Nucula_. ×450. Fig. 6. Section through the body of _Nucula_ showing the position of the cerebro-pleural ganglion cut through the center. Dorsal side up. The cellular portion of the ganglion is black. ×70. Fig. 7. Section through the body of _Nucula_ at the level of the visceral nerves which are shown on either side of the section. The area of nerve cells is shown in black. ×70. Fig. 8. Reconstruction from serial sections of the cerebro-pleural mass nerves and connectives of _Malletia faba_. The drawing is a ventral view, the cephalic side is at the top. ×70. Fig. 9. Reconstruction of pedal ganglion of _Malletia_ from the ventral side. Cephalic side at the top. ×70. Fig. 10. Reconstruction of visceral ganglia of _Malletia_. ×70. Fig. 11. Section through cerebro-pleural mass of _Malletia_. The dorsal side is up. On the ventral side to the left and right are the beginnings of the lateral lobes or ganglionic cords which may represent the pleural ganglia. In this species the cerebral ganglia are not separated into right and left halves as in _Nucula_. ×300. Fig. 12. Section through the central part of the pedal mass of _Malletia_. The dorsal side is up. ×300. Fig. 13. Section through one visceral ganglion of _Malletia_. The dorsal side is up. ×300. [Illustration] [Illustration] JOURNAL OF ENTOMOLOGY AND ZOOLOGY--_Advertising Section_ _The_ Journal _of_ Zoological Research _Edited by WALTER E. COLLINGE, M. Sc., F. L. S., F. E. S. The Gatty Marine Laboratory The University, St. Andrews, Scotland_ The subject matter is strictly confined to original zoological research--systematic and anatomical. Fully illustrated by lithographic plates and text figures. Each volume will consist of 4 parts, price $5. _All subscriptions should be forwarded to_ Messrs. Dulau & Co., Ltd. 37 Soho Square, London, W., England GRIFFITH Incubators [Illustration]