DIAGRAMMATIC SECTIONS. 119 



PLATE XVII. 



A series of diagrammatic sections illustrating 

 the different arrangement of the Branchiae in 



LAMELLIBRANCHIATA. 



Fig. 1. Transverse section of FIUBRANCHIATA. 



2. EULAMELLIBRANCHIATA. 



,, .- 



*- 



5.- 



6. 



PROTOBRANCHIATA. 



SEPTIBRANCHIATA. 



7. Showing a number of filaments attached to 

 interfilamentary junctions (interfil. ju.), which 

 are retained in loop form by expansions named 

 interlamellar junctions (interlam. ju.), a part 

 of each alternate loop being filled with 

 occasional interfilamentary septum. 



8, 9, 10. Portion of gill axis with filamentary rods. 



,, 11. Two rods with epithelial prominences, from 

 which project rows of long cilia interlocking 

 with others of adjacent filamentary rods. 



The LAMELLIBRANCHS constitute the primary division, 

 or Class, of the Phylum MOLLUSCA. A Lamellibranch is a 

 symmetrical mollusc which is devoid of head and 

 odontophore, or toothed tongue; the mantle, or covering 

 of the body, divided into two lobes ; the shell composed of 

 two parts, or valves ; and respiration, or oxygenation of 

 the blood, is performed by lamellate gills. The name 

 LAMELLIBRANCHIATA has been taken from the form which 

 the gills present in most members of this Class. The 

 Gills, or branchiae, are projections of the body, and are 

 usually placed in a part known as the mantle-cavity. 

 These branchiae take a certain form to which the term 

 Ctenidia has been applied. Each ctenidium consists of an 

 axis attached to the body, and bearing two rows of 

 projecting lamellae. These organs are an additional 

 assistance to the general system of respiration, which, in 

 all species of this class, is carried on through the outer 

 surface of the body. 



* I have not been able to determine these, ED, 



