236 On the Gastric Organs of Spirilla, Nautilus, etc. [Mar. 17, 



In Tanganyicia the valvular folds of the caecum are still more reduced. 

 In Strombus and Pteroceras there is a style-sac, but nothing com- 



SiQr. 4.— Gastric apparatus of Spirula, dorsal aspect. After Huxley. Letters as 



before. 



parable to a caecum; while in forms like Littorina and Vivipara there 

 is neither caecum nor sac. In the Lamellibranchiata there is often a 

 style-sac, sometimes no trace of this, and there is no spiral caecum. 



