338 



MOLLUSC A. 



V\ 



\j 



the outer row, and internal in the case of the inner filaments. The 

 adjacent filaments of the same row, both in their descending and 

 ascending limbs, are held together by the inter- 

 locking of some especially long cilia (Fig. 265, cj) ; 

 and the ascending and descending limbs of the 

 same filament are in some cases united by fusion 



of tissue at 

 certain points, 

 'giving rise to 

 the so - called 

 interlamellar 

 concrescences 

 (Fig. 266, ilj). 

 Further, the 

 ends of the as- 

 cending or re- 

 flected limb of 

 the outer fila- 

 ments may be 

 united to the 

 mantle, or may 

 be free (Fig. 

 264 B, C), and 

 similarly the 

 ends of the as- 

 cending limbs 

 of the inner 

 filaments may 

 be free, or 

 those behind 

 the foot may 

 be united with 

 their fellows a- 

 cross the middle 



line, thus forming a septum, which cuts off a supra- 

 branchial chamber from the general mantle cavity. 



In all the Eulamellibranchiata and in a few of 

 the Pseudolamellibranchs (Ostreidae, Lima, Pinna, 

 etc.), the neighbouring filaments of the same row, 

 in both their limbs, are united at certain points by interfilamentar 

 vascular concrescences (Fig. 267). The filamentous character is still 



FIG. 265. Transverse section through the as- 

 cending and descending limbs of two adjacent 

 gill-filaments in Mytilus (after Peck). The 

 two filaments are connected by a ciliary 

 junction in the upper part of the figure. 

 be blood-corpuscle ; ch chitinous layer ; cj 

 ciliary junction ; ep epithelial prominence 

 which carries the cilia of a ciliary junction ; 

 fe frontal epithelium ; lac lacunar (vascular) 

 tissue ; Ife 1 latero-frontal epithelium with 

 long cilia ; Ife" second row of the same. 





FIG. 206. One fila- 

 ment of the gill of 

 Mytilus (after Peck). 

 fil descending limb, 

 fol ascending limb of 

 the filament ; ilj in- 

 terlamellar concres- 

 cence ; ep position 

 of interfilamentar 

 ciliary junctions. 

 The ascending limb 

 ends freely in a hook- 

 like manner. The 

 apex or angle of the 

 filament is grooved. 



