MORPHOLOGY OF MELIBE 575 



ectoderm ; the muscle-fibres are arranged in a fashion like the 

 fibres in a basket (PI. 27, fig. 3). 



9. The muscle-cell consists of two sarcoplasmic regions each 

 containing an abundance of micromeres : those in the inner 

 region are larger (PI. 31, fig. 33, Ca) than those in the outer 

 region. The larger are called in the text macromeres. Each 

 of these micro-macromeric sarcoplasmic regions is invested 

 by a coarsely granular net -work (My, Sar). The nucleus is 

 placed centrally within the cell. Its chromomeres (K) are 

 scattered differently, i. e. sometimes around the periphery of the 

 nucleus (PI. 31, figs. 32, 33, PI. 37, fig. 82) and sometimes less so. 



10. There is no definite body-cavity. The body-cavity as it 

 exists corresponds to the primary body -cavity of 

 Lang (1896) or the perivisceral cavity of Sedgwick 

 (1898). 



1 1 . The alimentary canal consists of five regions : 



(1) The oesophagus with the non-glandular lining, and back 



of it the oesophageal glands or salivary glands (PL 32, 

 figs. 36, Oe, 41, Sg). 



(2) The proventriculus with distinct glandular lining 

 (PI. 32, figs. 36, G, 38, Gl). 



(3) The gizzard with its stomach-plates which are formed 



by the secretion of the epithelial lining (vide supra), 

 (PI. 32, figs. 37, 42, 43, Stpl). 



(4) The pyloric diverticulum with its glandular and ciliated 



and much corrugated surface, which secretion does 

 not keratinize as that of the gizzard (PI. 32, figs. 35, 

 39, 44). 



(5) The intestine with its large typhlosole protruding into 



the cavity from the ventral side, and glandular ciliated 

 surface (Pis. 32 and 33, figs. 40, 45, 46, 47). The 

 structure of the intestinal lining is unique as concerns 

 the fibrillar nature of the cytoplasm, the clearly 

 visible terminal bars, and the basement membrane ; 

 also, the non-convergence of the cytoplasmic portion 

 of the cilia on the nucleus. 



12. The liver ramifies all the parts of the body. Its secretion 



