30 JOURNAL OF MARINE ZOOLOGY AND MICROSCOPY. 



birds, for instance, the Kiwi lays an egg almost as disproportionate, 

 but considering the mode of parturition in the Cephalopods, it is 

 improbable that this is the true size of the embryo. In this the 

 animal must have emerged from the egg and swam about naked till 

 it assumed nearly its adult size, so that the first chamber here 

 represents one of the chambers in the middle of an Orthoceras shell : 

 possibly, the earlier shell was once present, but was cast off, as is so 

 commonly the case with these early Nautiloids. The inflated end of 

 the siphonal tube has no claim whatever to be called a protoconch, 

 since it is homologous with the little bulging portion at the end of 

 the siphuncle in Spirilla, and contained within" the ovicell. 



Spirula, then, is in its anatomy closely related to Sepia : its 

 protoconch tells us nothing, since forms widely separated possess 

 identically shaped ones ; the structure of the shell proves it to be 

 unique among shells yet described. If it occurred in ancient strata 

 then we might have considered it closely related to Nautilus, as 

 Linnaeus and Cuvier did (by the former, it was named Nautilus 

 spirula), and then, by the formation of a deposit on the under surface 

 we should pass to Spirulirostra,, then by the straightening of the 

 chambered portion we should derive the Belemnites ; but though in 

 a recent authoritative article this descent was actually insisted upon, 

 the Belemnites occur first in the earth's history, and the Spirula 

 last, so that with the evidence at present available we must reverse 

 the process, and derive Spirula from the Belemnites through 

 Spirulirostra. 



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