Oil the Tertiary Shells of the Amazons Valleij. 101 



9. Hoviogeny of t]ie Spermatic Vouches and Vasa Deferextia 

 with Segmental Organs. — In Tuhifex I have observed that in 

 the ninth segment no representative structure precedes the 

 spermatic pouches. They commence as nearly spherical in- 

 versions of the integument after the testis has attained some 

 size. The condition of tlie vasa deferentia in the Naididas is 

 important in connexion with relation to the segmental organ. 

 Their extreme simplicity (in which they differ notably from 

 the Saenuridfe) would never have suggested an homogeny with 

 the segmental organ as it commonly occurs. The common 

 form (in the ancestral unisegmental Chaetopod) from which 

 the excretory segmental organ, spermatic pouches, and vasa de- 

 ferentia have equally been developed was probably very simple. 

 This is indicated by the simple form of the segmental or- 

 gans in Polychfeta, and the simple form of the vasa defe- 

 rentia in Naididfe, as also the simple form of the spermatic 

 pouches in all. The excretory segmental organs and the vasa 

 deferentia of Sffiuuridffi are more closely related 5 and probably 

 the latter were differentiated from the former at a later period 

 in the development of the group than that at ^v^hich the sper- 

 matic pouches and the simple male ducts of Nats and Chceto- 

 gaster were evolved. It is remarkable that, in the case where 

 special genital segments are developed (the Naididse), both the 

 segmental organ and setae of these segments are of a more 

 primitive form than those of the common locomotive alimen- 

 tary segments ; whilst in Saenurid®, where the genital seg- 

 ments are present from the earliest period, and perform the 

 functions common to all the segments or somites, the setffi and 

 the segmental organ of one of the genital segments have the 

 usual character of locomotive and secretory organs. 



XII. — The Tertiary Shells of the Amazons Valley. By Heney 



WOODWAED, F.G.S., F.Z.S., of the British Museum. 



[Continued from p. 64.] 



[Plate v.] 



The following is a list of the specimens recorded by Mr. 

 Conrad. 



Gasteropoda, 



1. Isaa, Conrad. 4. Hemisinus, Swainson. 



/. Ortoni, Gabb, sp. H. sulcatus, Conrad, 



/. lintea, Conrad. .5. Dyris, Conrad. 



2. Liris, Conrad. D. r/racilk, Conrad. 



L. laqtieata, Conrad. 6. Neritina, lianiarok. 



3. Ehora, Conrad. N. Ortoni, Conrad. 



E. crassilabra, Conrad. N. jnipa, Gabb. 



3a, (Subg.) Nesis, Conrad. 7. Bulimits, Scopoli. 



N. bella, Conrad. B. linteus, Conrad. 



