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Give a short Description of the Gills of Astacus, indicating 

 their Position on the Body. What is the precise 

 Function of the Scaphognathite ? 



The gills are situated on both sides of the thorax, in the 

 branchial chamber (i.e., the space between the body- Avail 

 and the branchiostegite) ; they are soft, plume-like vascular 

 outgrowths. Each gill consists of a hollow stem and numer- 

 ous hollow filaments with thin walls, through which the 

 blood takes up oxygen from the water. The stem is divided 

 into two longitudinal vessels (afferent and efferent) with 

 which the filaments communicate. 



There are three sets of gills : 



1. The pleurobranchs resemble bottle- brushes. Arising 

 from the body-wall, above the last walking-leg, there is 

 a well-developed pleurobranch ; and there are rudiments 

 of two above the 3rd and 2nd legs. 



2. The arthrobranchs are like the pleurobranchs ; and 

 ;they arise in pairs from the membranes beside the bases 

 of the 2nd (one gill only] and 3rd maxillipedes, the chelae, 

 and the 2nd, 3rd, and 4th legs. 



3. The podobranchs have flattened and folded stems 

 -(epipodites) bearing the filaments ; and they arise singly 

 from the bases (coxopodites) of the 2nd and 3rd maxillipedes, 

 the chelae, and the 2nd, 3rd and 4th legs. The 1st maxilli- 

 ,pede has an epipodite only. 



The scaphognathite (of 2nd maxilla) occupies the front 

 ^nd of the branchial chamber, and, by its continuous 

 aji'.on, keeps a current of water flowing from behind for- 

 wards. 



NOTE. Nephrops has five podobranchs and a rudiment 

 (on 2nd maxillipede), eleven arthrobranchs, and four 

 .pleurobranchs. 



Write a general Account of the Internal Organs of Astacus. 

 A short gullet leads upward from the mouth into the 

 large stomach or gizzard ; and these parts constitute the 

 .lore-gut or stomodaeum. The mid-gut or mesenteron is a 

 very small area with a dorsal pouch or caecum ; and the 



