INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 953 



of a longitudinal striation, and it is soon possible to detect a striation 

 of its epithelial cells. The terminal kidneys are also appearing ; 

 these arc not developed, as has been often supposed, from the rectum, 

 but in a similar fashion to the other segmental organs, and, as they 

 belong to the terminal segment, their mode of development has an 

 important bearing on the theory of metamerism. Other points must 

 be passed over to bring us to the next stage in which the larval 

 characters begin to lose their importance, and the creature commences 

 to take on the more definite characters of the Echiurus. As these 

 processes are being completed the ciliary circlets get lost, while 

 blood-vessels and dermal papillte begin to appear. In the last larval 

 stage we have distinct, though young, Echiuri. 



Theoretical Considerations. — The author is of opinion that the 

 history of develoijment, as he has observed it, is conclusive as to the 

 Annelidan affinities of Echiurus ; and, as this genus has very distinct 

 relations to the other chfctigerous Gephyrea, Thalassema and Bonellia, 

 he believes himself justified in extending his generalizations to the 

 whole of the Echiurida. Every point of importance in development 

 is Annelidan, but we have farther to recognize that, owing to 

 adaptation to special modes of life, the Echiurida are modified forms. 

 The next question is, of course, are their relations to the Archi- 

 annelides closer than they are to higher forms ? and here their com- 

 plicated organization and the jDresence of the characteristic setai 

 enable us to answer it in favour of their nearer relationship being to 

 the Chastopoda. Further consideration leads us to see that by the 

 presence of a proboscis, the absence of distinct dissepiments, tho 

 reduction of the setoe and of the segmental organs, together with such 

 important j)oints as the extension of the post-oral region and the 

 characters of the terminal segments in which there is an organ 

 homodynamous with a segmental organ, the Echiurida have undergone 

 a wide divergence from the primitive type. 



As to their relations to the non-setigerous Gephyrea (Sipunculids, 

 &c.), the author is not completely satisfied, and waits for embryological 

 investigations to say whether some of their characteristics are due to 

 genetic relations. 



The Annelidcs may now bo thus arranged : — 



1st Class. Archiannclides (Polygordiua). 



2nd Class. Chaitopodcs. 

 1st Order. Saccocirrida3. 

 2ud J, Polycha;tiT!. 

 3rd. „ Echiuridic. 

 4th. „ Oligochicta;. 



3rd Class. Ilirudinea. 



Api)endix (1th Class). Sipuneulacea. 



As to their bearing en the Trocliophoro-thoory, tho author is of 

 opinion that the i)resent results bear out fully the doctrines on which 

 he has previously insisted ; while as to the theory of segmentation, 

 he points out that in tho IVIullusca there is a similar distinction 

 between head and trunk, but that no mutameric difiercntiation is to 

 be made out in the latter. In the hnver Bilateria the chief orfjians of 



