!'\ II U.S. 



explanation of tlio observed phenomena; bul ihat the characters, as in V 

 mann's thi ;■ or in pan could have affected the ovum when thev first 



appeared, does nol seem I ined l»_v the facts. The examples cited above 



of the transmission <>f the characteristics «>C the asiphonula and caecosiphonula 

 to the typombryo of the Ammonoidea give similar evidence w i 1 1 1 regard to the 

 mbryonic characters, and are directly against Weissmnnn's posil 

 B M ; er-Chalinas bave tried unsuccessfully to prove the abso- 



lute invariability of differentials among fossil Cephalopoda by means of the 

 apparent differences between the embryos <>i Nautiloids and Ammonoids, hut 

 the d • iii.li in Orthoceratidse lias demonstrated their ••nor. 1 



ami we confidently anticipate the discovery of some form in which the proto- 

 ibit intermediate characters. 

 The rostrum in the Ammonoids contrasts decidedly with the central .-inns of 

 of tin- aperture in Nautiloidea, and is a differentia] of importance, 

 which »e mentioned here. The rostrum of the mesozoic forms indicates 



!«• Vinmonoids iliil nol possess the ambulatory pipe <>r byponome 1 of Nau- 

 the ventral sinus in the aperture and Btriaa <>f growth in that 

 order. A- the) could not have been Bwimmers in the same sense as 



itilus, and they must have been for the most part strictly 1 

 crawl . babit of crawling as a Blower mode "t' progression combined with 



-. may bave been the cause of the higher spe- 

 cialization an i greater variety of forms and structures which thev exhibit. The 

 change from a ventral Binua to a rostrum in the aperture began among the higher 

 ileozoic time, and is shown by the narrower ventral sinus 

 of the aperture, and in the lines of growth on the .-hell. This .-inns also is more 

 \y marked, and i- present oftener, in the devonian forms of Goniatitinaa 



than in ti. 



Clymeninaa of the Devonian have very -mall ventral Binuses in many 

 the hyponome may have been absent. The specimens ob- 

 ithor hav< rule exhibited the lines of growth with 



the striatums, and in some sp 

 they : the venter The Ammonoids <>! the Trias are appar- 



ently med, the rostrum and the ventral saddle in the lines 



r, ponome. 

 ilatorv byponome disappeared, all the sutures became more 

 complicated or lal, and, in correlation with the greater lengthening 



ntral zone <>i the mptum changed from con- 

 When one ' Ltribute th ngin of convexity in the 



the multiplication and lengthening of lobes, <>r the marginal d 

 lions of thi irtuitous variations, he finds a( 



with the phenomena 

 of morphological eq '. t \ «■> 1 by Von Buch, and 



. . 

 Ill . K 



