86 B ALANINE. 



of the stomach, which would serve to expose the food to a 

 greater extent of digesting surface.* 



As in the case of the Lepadidse, a transparent, structure- 

 less, epithelial tube, composed of chitine, containing more 

 or less digested food, is found, in specimens preserved 

 in spirits, occupying the whole length of the stomach, 

 and where there are cseca, sending branched prolonga- 

 tions into them. It does not extend into the oesophagus 

 or into the rectum. This epithelial tube or model of the 

 stomach, filled with excrement, is expelled by the rectum, 

 whole, that is in a single piece, as I observed in some living 

 specimens of Balanus balanoides : in some specimens, how- 

 ever, of Chthamalus stellatus, the excrement was ejected, per- 

 haps from the animal being confined, in fragments, and the 

 sack thus became befouled. Beneath the epithelial layer, 

 the stomach is lined by a delicate, pulpy and cellular mucus 

 layer, which easily peels off in flakes : this is surrounded 

 by a muscular layer with the fibres closely approximated and 

 transverse; and this by a layer of stronger, longitudinal 

 muscles, but more distant from each other. Lastly, outside 

 this double muscular layer, there is a rather thick, somewhat 

 laminated, pulpy layer, abounding with cells, often nu- 

 cleated, and frequently containing much oily matter. This 

 structure agrees closely with Dr. C. H. Jones'sf account of 

 the external covering of the stomach in Daphnia, and which 

 he believes to be hepatic : as in Daphnia, there does not 

 seem to be any ducts. I may here observe, that within the 

 upper part of the prosoma, but not immediately connected 

 with the stomach, I have often observed much white pulpy 

 substance, permeated by lacunal passages, and exhibiting 

 no structure except some excessively minute cells. 



* The presence and absence of these caeca in genera so closely allied as 

 Balanus and Tetraclita, shows, T think, that these cavities are not of high im- 

 portance; and I must doubt whether Von Siebold's view (' Anatomie Comparee,' 

 torn, i, p. 4-A5), that these caeca form a passage to a true or isolated liver, such as 

 exists in the higher Crustacea, can be admitted. Caeca are said by Von Siebold 

 to occur in some of the Entomostraca, as Daphnia, Argulus, &c. 



t 'Philosophical Transactions,' 1849, p. 11G. Karsten ('Nov. Actorum 

 Acad. Nat. Cur.,' 1845, tab. xx) has excellently figured the testes, as the 

 hepatic glands ; and has indicated the ovaria as salivary glands ; it is singular 

 that this anatomist overlooked the ducts which lead from his supposed hepatic 

 glands, into the vesiculse semiuales, within which he observed spermatozoa. 



