JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATE XXXIV, 



Illustrating Mr. Mitsukuri's Memoir on the " Structure 

 and Significance of Some aberrant Forms of Laraelli- 

 branchiate Gills." 



NUCULA. 



Fig. 1. — The view of the soft parts of a male specimen, the left valve 

 having been removed, and the left lobe of the mantle cut away along the 

 lower border of the visceral mass near the line ay. Enlarged about seven 

 times. 



a. a. Anterior adductor, p. a. Posterior adductor, v.m. Visceral 

 mass. f. Foot. g. Gill. I. Labial palpi. La. Tentacular append- 

 age of the labial palpi. Lb. Huod-like appendage of the labial pa!|)i. 

 m. Membrane suspending the gill, and attached to the body along the 

 broken line xy zw. p. Posterior end of the gill. 



Pig. 2. — Posterior part of the labial palpi of the right side, showing the 

 arrangement of labial appendages. Diagrammatic. Letters same as in 

 Pig. i. 



Fig. 3. — Diagram of the membrane suspending the gill. Seen from 

 al) )ve. Letters of the same significance as in Pig. 1. 



Pig. 4. — The gill of one side dissected out and drawn by itself. Seen 

 from below and slightly from one side. Enlarged about thirty-five times. 

 X. Anterior end. p. Posterior end. xcp. Line of suspension. 

 xdp. Ventral median line, .tap and x b p. Parts projecting down- 

 ward of the plates composing the gill. 



Pig. 5. — An opposed pair of the plates composing the gill. Enlarged 

 110 diameters. The columnar epithelium cells represented in the figure, 

 along the borders a d and /} d, are the optical section of the characteristic cells 

 found around the edges, and therefore the surface of the irregularly rect- 

 angular cells just inside ought to be continuous with the outer edge of the 

 columnar cells, but is not so represented in the figure in order to avoid 

 confusion. The cubical cells along the borders ia and j^'/i are also shown in 

 optical section in a similar way. The coloured part is the chitinous frame- 

 work. Por the sake of clearness, cells are filled in larger than they 

 should be. 



kijL Suspending membrane of the gill. idj. Stem which is con- 

 tinuous along the whole length of the gill. Seen here in cross-section. 

 e. Plates which project downward from the stem i dj, and which are 

 the proper respiratory organ, n. Lower blood-channel in the stem. 

 0. Upper blood-channel in the stem. *. Trough of the chitinous 

 framework. This is continued throughout the length of the gill. 

 Seen here in cross-section. c.p. Crosspiecc ihat divides the trough 



