No. 2.J FILAMENTS IN THE LAM ELLIBRAXCH GILL. 79 



As regards the size and finer structure of the filaments, the 

 evidence of sections is more reliable than that of surface prep- 

 arations ; and in Figs. 4-8 are represented a series of sections 

 through a group of filaments of the inner gill of Cardinm ednlc. 

 The same filaments are shown in all the figures, although the 

 very complex interfilamentary and interlamellar connections, 

 differently cut in the different sections, cause a considerable 

 variety of aspect. These connections may be disregarded in 

 the present discussion. In Fig. 4, which represents the upper- 

 most section, six filaments are shown, all practically alike. In 



FIG. 7. FIG. 8. 



FIGS. 4-8. Series of sections through group of filaments of inner gill of Cardium edule. x 95. 

 Cilia and nuclei somewhat diagrammatic. Fig. 4 is uppermost section. Asterisk marks 

 two simple filaments fusing to one compound. 



Fig. 5 two of these, marked with an asterisk in all the figures, 

 show a slight modification of the epithelium, as described above. 

 This section is immediately above the point of fusion of the 

 two filaments. Fig. 6 shows these filaments so closely approxi- 

 mated that they may almost be described as forming a single 

 deeply grooved filament, a condition better shown by other 

 preparations. In Fig. 7 the fusion is complete, but the com- 

 pound filament is still considerably enlarged; while in Fig. 8 

 the compound filament has regained its normal size and form, 

 and the transition is complete. 



Strangely, this very conspicuous fusion of the filaments 

 appears to have received little or no notice. I have been able 

 to find no reference whatever in the text of any articles at my 



