52 AMERICAN JOURNAL 



Alimentary canal without a differentiated stomach; usually 

 straight with a posterior anus and anterior mouth, but these lat- 

 ter characters do not apply to some of the Gephyrea, which have 

 a mouth which is not anterior, an anus either anterior or pos- 

 terior, or no anus at all ; with a convoluted intestine. 



Terrestrial, fluviatile or marine in habitat. 



The above very qualified diagnosis well illustrates the prevail- 

 ing diversity of the forms of this type, and may itself require 

 further qualification. The only portions of it which appear to 

 be essentially universal are those in italics. 



The subclass Gepliyrea contains many aberrant forms, once 

 associated with the Trepangs. The greatest variations occur in 

 this group. Jourdain* found in four species of Sipunculi three 

 without an anus and the other with a posterior anus. Kefer- 

 stein and Ehlersf describe Sipunculus nudus and tesselatus as 

 having a posterior anus. The Aspidosiphonido? are characterized 

 by a dorsal anus, the Loxosiphonidai by a terminal anus,| and in 

 the other groups this character varies greatly. Most of these 

 forms have colorless blood, as do all the Aphroditacea (and many 

 others) among the typical Annelids § 



The "segmental organ" described by Dr. Williams, || its dis- 

 coverer, as prevailing " throughout the Actiniidce (Aealephce) 

 Echinodermata, llotifera and Annelida" is stated by Claparede^[ 

 to be wanting in some Annelids, or reduced to simple apertures 

 in the wall of the body, or wanting an, internal orifice, as in 

 some Capitellea ; it also exists in the anterior segments of many 

 Annelids in which the genital products do not penetrate to that 

 region. Its wall is often glandular and it can hardly be doubted 

 that it also plays an excrementitial part. In the Oligocholia only a 

 small number of these organs are modified for the purpose of con- 

 ducting outward the sexual elements, while the rest incontestably 

 fulfil other functions. The same is true of the Polychoeta. The 

 " porenkanale" occur only in the species with a thick cuticle, 

 and not even in all these. They are tubular pores correspond- 

 ing with subadjacent cells. (Claparede, loc. cit.) 



Pores for the discharge of certain secretions appear to exist 

 in all species of Annelids. (lb.) 



* Comptes Rendus, April, 1867, p. 871-3. 



tBull. Sci. 1861, p. 387. 



JBaird, P. Z. S., 1868, pp. 76-114. 



§Oweu, Comp. Anat. Inv. p. 246. 



|| Froc. Royal Soc viii, p. 371-6, 1857. An. Nat. Hist., Second Ser., 

 xix, p. 393-7, 1857. 



fl Annals Nat. Hist. 3d Series, xx, p. 355-6, 1867, and Biblioth. Univ. 

 Arch. Sci. p. 1-44, Sept., 1867, and also in Introduction to his work on 

 the Annelids of the Bay of Naples, 1868. 



