694 



DEEP WATEE MOLLUSKS AND BEACHIOPODS—DALL. vol.xvii. 



are distinctly inarginated, as in JSfncula, but are connected together 

 by small patches of what appeared to be fibrous tissue, which proves 

 to be interlocked giant cilia (see fig. 2, vi). Owing to the oblique 

 manner in which the plates are set on the stem, and the manner 

 in which they are tied together, it is difficult to get a section which 

 will show the whole face of any single lamella and determine exactly 

 how many ciliary bridges exist to each i)late, but the distal margins 

 of the x>lates were free from each other for some little distance 

 inward. The outer edges of the lamellae appeared to be furnished with 

 a small circular band of muscular fibers by which the periphery might 

 be contracted, but no rigid chitinous framework could be detected. 

 Along the channels between the series of plates were accumulations of 

 dark-colored organic granules, indicating that the ctenidia perform the 

 function of collecting food material. 



After using a low-power lens in dissecting- in the ordinary way, 

 serial sections with the microtome, after hardening and staining, were 



resorted to, in or- 

 der to get at the 

 structure of these 

 and other organs. 

 Dr. Gray, micro- 

 scopist of the 

 Army Medical 

 Museum, kindly 

 undertook the 

 manipulation a :d 

 mounting. It was 

 found that the 

 X)rocesses requir- 

 ed, as preliminary 

 to section izing. 

 Fig. 2. were destructive 



MICROTOMIC SECTION OF PORTIONS OK THE GILL OP EUCIROA PACIFICA.* Ot UiaUy ClellCate 



feat ures which 

 with the dissecting microscope are easily observed in fresh mate- 

 rial. On the other hand, the sections (shriveled and distorted as 

 they are, compared with fresh specimens) exhibited a number of 



* Figure 2 ; section of the plates of the inner reiiecteil lamina of the gill of Euciroa 

 pacifica, greatly enlarged, from microtomic section at a tangent to the anterior sur- 

 face of the posterior adductor, camera lucida drawing by J. C. McConnell. 



I, II, combined plates at tlie point of reflection, defective above; III, IV, mass of 

 connective tissue, etc., forming the junction of the right and left ctenidia behind 

 ti e foot; V, V, V, plates which have been torn by the knife in cutting, simulating 

 vascular connections ; VI, giant cilia connecting the plates distally ; VII, VIII, plates 

 connected by a true vascular junction. 



For a proper conception of the real relation of the parts before shriveling by the 

 staining process, the reader should refer to pi. xxiii, fig. 2. 



