No. I.] LARVAL STAGES OF SCHLOEiXBACHIA. 241 



probable relationship of these genera and the meaning of the 

 growth stages. From the researches of Hyatt, Branco, and 

 Karpinsky we have learned that the ammonoids preserve in 

 each individual a complete record of their larval and adolescent 

 history, the protoconch and early chambers being enveloped 

 and protected by the later coils of the shell. Thus by break- 

 ing off the outer chambers successively the naturalist can, in 

 effect, cause the shell to repeat its life history in inverse order, 

 for the ontogeny of the individual is an epitome of the history 

 of the race, and each stage of growth represents, if not always 

 an ancestral genus, at least some of the salient characters of 

 that genus, although unequal acceleration often crowds together 

 in an ontogenic stage characters that occurred in genera widely 

 separated in time. But where the parallelism is at all exact 

 these genera appeared (although not necessarily disappeared) in 

 the order of their minute imitations in the larval history of 

 their descendants ; thus by comparing larval stages with ante- 

 cedent adult forms the naturalist finds the key to relationships 

 and is enabled to arrange genera in genetic series. 



The ammonoids were all marine, never parasitic, never fixed 

 in station, and with them no resorption of the shell has ever 

 been noted; thus with them, while there often is some slight 

 obscuring of the record, due to unequal acceleration of certain 

 characters, there is no "falsification of the record." Ancestral 

 characters may not be repeated in the same association in the 

 history of the descendants, but they occur in the same order in 

 which they occurred in the history of the race. So far as the 

 writer's experience goes, these characters shown in the larval 

 stages of ammonites are mainly palingenetic ; it is a mistake to 

 give the name of coenogenesis to crowding together by unequal 

 acceleration in the descendant of characters that occurred in 

 separate generations of ancestors. 



Omission of stages. — The only cases known to the writer 

 where stages of growth are actually omitted entirely are : (i) by 

 pushing back remote ancestral stages or characters beyond the 

 protoconch, where they are either lost entirely out of the ontog- 

 eny, or at least leave no record in the shell; (2) between the 

 protoconch and the first larval stage. The protoconch is remark- 



