ARTHROPOD A. 35 



part of the meso-pyloric ossicle has been removed, so as 

 better to exhibit the 'pre-pyloric ossicle' which lies beneath 

 it. The post-cardiac process and the uro-cardiac ossicle, with 

 its teeth, are also best seen in this specimen. The supero- 

 lateral ossicle sends inwards from its inferior border a strong 

 calcined process, which carries on its internal face the large 

 lateral gastric tooth. On the infero-lateral parietes of the 

 stomach there are several rod-like ossicles. To the inferior 

 extremity of one of these, the ' lateral cardiac/ stretching down- 

 wards and backwards from the 'ptero- cardiac,' is attached a 

 small ossicle, which internally bears a bifid tooth. The under 

 surface of the stomach is strengthened by two nearly parallel 

 rods, which extend from the pylorus forwards to the cardiac 

 division, where they become divergent and more or less mem- 

 branous. Their posterior extremities, also slightly divergent, are 

 somewhat thickened, and each articulates with two rods, one 

 of which is connected with the ossicle just described as bearing 

 the bifid tooth, while the other joins the ' supero-lateral ossicle.' 

 There are thus five gastric teeth, one median, and two lateral 

 on each side. 



In A, on looking into the gastric cavity and towards the 

 pylorus, we can see, situated beneath the median gastric tooth, 

 a bilobed valvular process; and on either side, immediately 

 beneath the great lateral teeth, is a similar cushion-like process. 

 These processes are beset with hairs, and by their mutual 

 apposition form an efficient sieve to prevent the undigested 

 food from passing into the intestine. 



For an account of the structure and functions of the stomach 

 of Astacus fluviatilis, which differ but little from that of the 

 specimen described above, see Huxley, "Medical Times and 

 Gazette" 1857, Vol. xiv. p. 255 : also Rolleston, p. 90. 



50. The cephalo-thorax and the first fourteen segments 

 of a Langouste (Palinurus vulgaris.) 



The same numbers have been affixed to the same parts as in 

 the preceding specimen : and the description is in the main 

 equally applicable. 



51. A Lobster (Homarus vulgaris), dissected to shew its 

 nervous system, which is of the type termed ' homogan- 

 gliate:' that is, it consists of a longitudinal series of ganglia 



32 



