Fissiparous Species of Tubicolar Annelid. 121 



walls than the remainder of the alimentary canal (fig. 5). The 

 crop communicates by a constricted portion with a wide stomach, 

 whose walls are strongly tinged by deep brown granules. This 

 passes into a narrow intestine, which widens in the caudal 

 region into a sort of rectum, opening externally, between the 

 terminal papillae, by a richly-ciliated anus. 



In every segment the intestine was united to the parietes 

 by delicate transverse membranous dissepiments, forming par- 

 titions across the perivisceral cavity, aod thus dividing it into 

 a series of chambers, which, so far as I could observe, did not 

 communicate with one another, though it would be unsafe ab- 

 solutely to affirm this. 



"Vascular" System. — The so-called " blood"- vessels* of 

 the Annelida were represented, in the present case, by 

 lateral contractile vessels which ran upon each side of the 

 intestine, and gave off transverse branches on to the dissepi- 

 ments, from which twigs proceeded dorsally and ventrally. 



The dimensions of these lateral vessels varied considerably : 

 sometimes they were comparatively narrow, but in other in- 

 stances so wide as to appear to form a complete sheath around 

 the intestine. They contained a deep green, clear fluid, to- 

 tally without corpuscles or solid elements of any kind, while 

 they themselves, when empty, were usually quite colourless ; 

 but I would draw attention to the curious fact, which I have 

 also observed in other annelids, that in the anterior part of their 

 course they occasionally present bright green, granular par- 

 ticles, imbedded in, and adhering to, their outer surface. 



The opacity of the anterior end of the animal, resulting 

 from the quantity of deep red pigment, prevented any very 



* At the last meeting of the British Association (September 1854), I ven- 

 tured to propound the theory that what are commonly called the blood- 

 vessels of the Annelida are not " blood"-vessels at all ; that is, that these ves- 

 sels, and the fluid which they contain, are not the homologues of the blood- 

 vessels and blood of Vertebrata, Mollusca, and Articulata, the latter being 

 represented in annelids by the perivisceral cavity and its contained fluid, 

 whose anatomical and physiological importance have been so excellently and 

 exhaustively developed by De Quatrefages. See his researches on the Anne- 

 lids, and more particularly his memoir " Sur la cavite generale du corps des 

 Invertebres." It is to be hoped that M. de Quatrefages understands that in- 

 structed Englishmen do not countenance the unwarrantable attempts that have 

 been made to depreciate his merits in this country. 



