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over the latter, investing it closely for the greater part of the length 

 of the somite. In cleared mounts it appears as a brownish, almost 

 opaque, mass filling the greater part of the ccelom at the above-men- 

 tioned point. It is a single organ with two shallow longitudinal de- 

 pressions, one dorsal, and the other ventral, the former being the more 

 distinct. Sections (PI." VIII, Figs. lo and ii) show the organ to be 

 made up of a series of branching, rather thick-walled tubules, about 

 twelve in number, which extend radially and cephalad. The region of 

 the digestive tract (PL VIII, Fig. lo) from which these tubules arise 

 is ciliated, and the basal parts of the lumina of the latter are also 

 ciliated. These tubules give off branches as they extend anteriorly, 

 until the whole mass of the anterior part of the organ is composed of 

 the finer tubules, which lie in very close proximity to each other. The 

 walls of these tubules are distinctly nucleated and appear to be com- 

 posed of glandular tissue. The whole diverticulum is invested in a 

 peritoneal layer, beneath which is a very much reduced muscle layer — 

 a continuation of the muscle layer of the digestive tract. The 

 perivisceral blood sinus appears at the point of origin of the tubules 

 from the digestive tract. This sinus is continued cephalad, and the 

 reduced spaces which appear between the tubules of the diverticulum 

 are continuations of this sinus. In all of the specimens studied the 

 structure of this organ is uniform in all respects. 



The presence of the mid-dorsal and mid-ventral longitudinal grooves 

 suggests the possibility that this organ may have developed from two 

 lateral outgrowths from the digestive tract which came together, fus- 

 ing at the points of contact; but an examination of the point of origin 

 of the diverticulum shows no evidence that it arose as two separate 

 parts. 



Dorsal Blood-vessel. — The dorsal blood-vessel arises from the 

 perivisceral blood sinus in IX. In some of the specimens it shows a 

 conspicuous expansion in IX, immediately after it originates from 

 the sinus ; but this is not a constant feature, since some specimens do 

 not show it at all, while others show only a moderate expansion. 



Neplwidia. — The first nephridia are related to V/VI. There is 

 some variation in their size and shape in the various specimens and 

 in the different regions of the body, although this variation is within 

 rather narrow limits. The anteseptal part (PI. VIII, Fig. 2) is re- 

 duced in size, the postseptal part being about two and one-half times 

 larger. The efferent duct arises near the septum and is longer than 

 the postseptal part. 



Spermiducal Funnel. — The small spermiducal funnel (PI. VIII, 

 Fig. 4) is situated in the posterior part of XI, with its base in close 



