2*4 ANIMAL BIOLOGY. [Part II. 



2. Between these two in the mid-line 



(c.) An anterior median bar, the urocardiac, passing down- 

 wards and backwards, the posterior end of which 

 (see B.) has two oval brown convex surfaces. 



(d.) A posterior median bar, the prepyloric, passing 

 downwards and backwards from the anterior edge 

 of the pyloric to the posterior end of the uro- 

 cardiac. Its ventral end carries a large brown 

 bifurcated median tooth. This ossicle is shown 

 in A. dotted, as seen through the transparent 

 pyloric. 



3. Between the transverse plates on either side there are 



(e.) On each side of the cardiac a small curved an- 

 terior lateral ossicle (pterocardiac). 

 (/.) Between the ventral or outer end of each ptero- 

 cardiac and the pyloric plate, a large posterior lateral 

 bar the zygocardiac. This has a strong projection 

 into the cardiac cavity, carrying a series of power- 

 ful brown lateral teeth. 



The main muscles connected with this apparatus are (1) the 

 anterior and posterior gastric (see 75, a. g. and p. g.), which, by 

 their contraction, tend to separate the transverse plates; and 

 (2) the cardiopyloric (c. p.\ which tend to approximate these 

 plates. When the plates are drawn apart (see 76, C.) the lower 

 end of the prepyloric, with its powerful median tooth, is drawn 

 downwards and forwards. At the same time the zygocardiacs, 

 with their strong lateral teeth, are swung inwards by the curved 

 pterocardiacs ; so that the median and lateral teeth clash in the 

 middle line. This the student will readily see when he experi- 

 ments with the stomach he has removed and cleaned with 

 potash. 



The filter cannot here be minutely described. The student 

 will, however, readily see how the canal is closed in by valves 

 and by the approximation of its walls, being indeed reduced to 

 a narrow triradiate slit. At the opening of the pyloric portion 

 into the intestine there is a median dorsal, and on each side two 

 lateral, pyloric valves. Here the chitinous lining ceases, and a 



