76 Journal of Entomology and Zoology 
there was more the appearance of four ganglia in the cerebro-pleural mass, and the 
ganglia seem less complex than in Malletia. This last species has more separate 
pleural ganglia, if the ganglionic cords can be so regarded. 
In neither of the species studied were all parts of the connectives easy to follow, 
so it was impossible to test the suggestions of Drew, but in both species there is 
some indication of two lateral lobes of the cerebral mass, and in Nucula there is good 
evidence of two central ganglia as well as the smaller lateral ones. The lateral 
ganglia of the cerebral mass are most clearly separated in Malletia. In Nucula the 
lateral ganglia are larger in proportion and the distribution of the gray and white 
matter is more irregular. 
REFERENCES nt 
Drew, G. A. 1901 
The life history of Nucula delphinodonta. Quart, jour. sc. vol. 44, pt. 3. 
Pelseneer, P. 1891 
Contribution a l’étude des Lamellibranchs. Arch. d. biol. xi. 
Stempell ‘ 1899 
Zur Anatomie von Solrmya togata. Zool. Jahrb. Bd. xiii. 
(Contribution from the Zoological Laboratory of Pomona College) 
EXPLANATION OF FIGURES 
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 once 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. X70. 
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. X300. 
Fig. 3. Section of the pedal mass of Nucula, through the center. The dorsal side 
is up. X300. 
Fig. 4+. Left side of the visceral mass of Nucula. Dorsal side up. X300. 
Fig. 5. Nerve cells from the central nervous system of Nucula. X450. 
Fig. 6. Section through the body of Nucu/a showing the position of the cerebro- 
pleural ganglion cut through the center. Dorsal side up. The cellular portion of 
the ganglion is black. X70. 
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. X70. 
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. X70. 
Fig. 9. Reconstruction of pedal ganglion of Malletia from the ventral side. Ce- 
phalie side at the top. X70. 
Fig. 10. Reconstruction of visceral ganglia of Malletia. X70. 
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. X300. 
Fig. 12. Section through the central part of the pedal mass of Malletia. The 
dorsal side is up. X300. 
Fig. 13. Section through one visceral ganglion of Malletia. ‘The dorsal side is up. 
X300. 
