jg 4 DESCRIPTIONS OF PREPARATIONS. 



where the chitinoid coat is divided into areae corresponding, as on the carapace, to 

 the individual cells. The cuticular coat of the stomach ends at the pylorus with 

 five projecting processes ; that of the intestine commences with six elevations pro- 

 longed into ridges which traverse the tube in a spiral fashion. Beneath the chitinoid 

 coat is the single layer of chitinogenous, or ectoderm cells, large in size, and then a 

 fibrous membrane followed by a layer of cellular connective tissue which incloses 

 muscle fibres, both longitudinal and circular, in the stomach and intestine. 



The chitinoid layer of the stomach is thickened in the dorsal and lateral walls 

 to form certain ossicles which, according to Vitzou, have the same structure as 

 Jthe carapace. Some of these ossicles have simply a supporting function, others 

 constitute the 'gastric mill.' The latter are named and arranged as follows. There 

 is a cardiac ossicle crossing the cardiac region transversely, articulating laterally 

 with a ptero-cardiac piece, and extending forwards into a softer disc upon which the 

 anterior gastric muscles are principally inserted, and backwards into a narrow uro- 

 cardiac piece which is produced inferiorly into two accessory or cardiac teeth, rudi- 

 mentary in the Lobster. A pyloric ossicle crosses the pyloric region transversely and 

 dorsally, and gives insertion to the posterior gastric muscles. It articulates in front with 

 a prepyloric ossicle which is bent downwards so as to form with it an acute angle 

 backwards way, and articulates in turn with the urocardiac piece (supra). Close to this 

 articulation the prepyloric ossicle is produced into a bifid median tooth, single in 

 the Lobster. The pyloric ossicle articulates laterally on each side with a zygocardiac 

 ossicle lying in the walls of the cardiac region. This ossicle articulates at its outer 

 extremity with the corresponding extremity of the ptero-cardiac ossicle (supra] of its 

 own side. Its inner extremity bears the great serrated lateral tooth. Just below the 

 anterior end of this tooth projects an infero-lateral tooth borne by the 'lateral 

 cardiac piece' of Milne-Edwards, one of the supporting bars of the stomachal 

 walls. The stomach possesses extrinsic and intrinsic muscles. The former set 

 includes the gastric muscles above mentioned, as well as the anterior lateral, the pos- 

 terior, superior and inferior dilators. The latter set includes various muscles. One 

 system of fibres unites the ptero- and zygo-cardiac ossicles. The remainder, according 

 to Mr. T. J. Parker, act as constrictors, especially a layer which embraces the pyloric 

 region. This region has its cavity, more particularly in the posterior part, narrowed 

 by the bulging inward of its side-walls and the development of a median ventral 

 ridge. The surfaces of these parts are beset with setae and form a most efficient 

 ' filter.' 



There is on either side of the stomach, at the entrance of the oesophagus, a 

 round white spot caused by the presence of a flattish papilla having the same 

 structure as the rest of the wall of the stomach. Forty days before a moult in the 

 adult, or for a shorter period in the young according to age, the chitinogenous cells 

 of this papilla develope a number of minute knobbed processes which raise the 

 overlying chitinous cuticle and eventually break up into corpuscle-like bodies. 

 Beneath the cuticle, and between the ends of the chitinogenous cells and their pro- 

 cesses, lamellae of calcified organic matter are laid down forming the gastrolith. 

 The lamellae are pierced by pores. Their substance consists of Calcium carbonate, 

 with a small admixture of phosphate, and of organic substances partly soluble in water, 

 partly insoluble, and perhaps chitinoid in nature. During the development of the 

 gastrolith the papilla becomes more prominent and changes its shape. The fully 



