370 



E. RAY LANKESTER. 



it correspond in any way to the sac in which the internal 

 shell of Limaz, and, further, that in which the pen of the 



Diagram of Loxosoma. m. Mouth, si. Stomach, shs. Shell-gland. 



Dibranchiate Cephalopods, is developed ? These two heads of 

 the question must be kept apart. 



We know, among Aplasia and its allies, and, further, in 

 Spirula, of external shells which have become internal, or, 

 we should better say, enclosed, by the overgrowth of the sur- 

 rounding folds of the mantel. That is apparently the indi- 

 vidual history of the concealed shell of Aplt/sia, and probably 

 is that of the concealed nautiloid shell of Spirula also ; and, 

 consequently, it may be inferred that such is also the genea- 

 logical history of those shells. 



But the development of Limax, Sec, has been sufficiently 

 studied by Gegenbaur (' Zeitschr. f. Wiss. Zool.,' Bd. iii), 

 and Schmidt (' Archiv f. Anatomic,' 1851)., to show that 



