ABERRANT FORMS OF LAMELLIBRANCHIATE GILLS, 595 
On the StructURE and SIGNIFICANCE of some ABERRANT 
Forms of LAMELLIBRANCHIATE Giuts. By K. Mrrsv- 
KuRI, Ph. B., of Tokio, Japan, late Fellow of the Johns 
Hopkins University, Baltimore. (With Plate XXXIV.) 
Tue following contribution to the morphology of the 
Molluscan branchie is part of an investigation on which 
I have for some time past been engaged, under the direction 
of Dr. W. K. Brooks, in Professor Martin’s laboratory at 
the Johns Hopkins University. The gills, of which the 
description is here given, are those of Nucula proxima and 
Yoldia limatula. They are extremely interesting because 
of their simple structure, and this account of their minute 
structure is published with the hope that it may throw 
some additional light on the nature of Lamellibranchiate 
gills. I wish to express here my sincere thanks to Dr. 
Brooks for his constant advice and assistance. I am also 
deeply indebted for specimens used in the investigation to 
Professors A. E. Verrill and 8. J. Smith, of Yale College, 
and to Mr. Richard Rathbone, of the United States Fish 
Commission. 
Nucula proxima, Say. 
This Lamellibranch shows many departures from the 
structure which is generally regarded as characteristic of 
the class. Fig. 1 gives a fair idea of what is seen when the 
left valve of the shell has been taken away, and the mantle 
of the same side removed along the lower border of the 
visceral mass near the line vy. a.a. is the anterior abduc- 
tor muscle made up of several fasciculi; p. a. is the posterior 
abductor. It will be noticed that Nucula possesses one of 
the few shells in which the umbo is turned toward the 
posterior end. In the specimen figured, the visceral mass 
(v. m.) shows convolutions on the surface, which, under the 
microscope, proved to be the male reproductive organ, pro- 
bably enormously developed for the breeding season, and 
this character enables one to distinguish the sex of a speci- 
men without difficulty. All the males have these convolu- 
tions, and, when preserved in alcohol, are of a greyish colour. 
The females show hardly any convolutions, and are much more 
darkly coloured. The foot (f) is folded longitudinally at 
its end, and can accordingly be spread out into a flat circu- 
lar disc. The labial palpi (/) are unusually developed, and 
-might at first sight be taken for gills. The inside of the 
