OXFORD UNIVEESITY SPITSBERGEN EXPEDITION. 1115 



conceived them as a rudimentary kind of organs of the first 

 type.^ 



Whether all these structures should go by the same name — 

 whether they are all modifications of one original structure — • 

 seems doubtful. Those of the second type are quite possibly 

 nephridia. It will be remembered that the Enchytrseids ha.ve, as 

 a rule, no nephridia in the first six segments (Bretscher (2) has 

 established a separate genus for a worm in which the fi.rst 

 nephridium occurs in segm. iii., the funnel being in ii.) ; and the 

 occurrence of dorsal and ventral " peptonephridia" in segm. vi., 

 extending thence, it may be, forwards or backwards, or both 

 forwards and backwards, their obviously similar constitution, and 

 their fundamentally paired nature would seem to justify the 

 assumption that they are really the nephridia of segm. vi. whicli 

 have become associated with the oesophagus. If, however, we look 

 on both dorsal and ventral organs as fundamentally paired (as we 

 seem justified in doing, v. ant.), we should then have two pairs of 

 nephridia belonging to segm. vi. In H. hrucei, in addition to 

 dorsal and ventral " peptonephridia "in segm. vi., there are also in 

 the same segment — indeed in the same section- — a pair of ordinary 

 nephridia (the first nephridium being here in segm. vi. with the 

 funnel in v.), i. e., thi'ee pairs in the one segment. 



Whether the organs discharge an excretory substance into the 

 oesophagus, or a digestive juice — or, indeed, whether they discharge 

 anything at all,- — is doubtful. Cejka says that the openings are 

 always hard to find in sections ; from which phraseology it would 

 seem doubtful whether they actually have definite mouths ; Welch 

 does not mention any openings, nor have I found any in my pre- 

 parations. On the whole, they are perhaps more likely to be 

 excretory, since they have an intimate relation to the blood- 

 spaces (in H. Jepiodera they run in the (esophageal sinus and are 

 directly bathed by the blood (Cejka, 4) ; in Hepatogaster also they 

 are bathed by the blood in the sinus, which may penetrate 

 between the individual cells ; I have found the same conditions, 



But the nephridial nature of the first group of organs, which 

 have for long passed under the name of "peptonephridia" — the 

 sinuous or coiled tubes which extend back, from the pharynx, 

 free in the ccelom — seems doubtful. These do not show the 

 peculiar structure of the Enchytrseid nephridium ; they have no 

 internal opening ; indeed, the only feature thn,t is brought forward 

 to substantiate their nephiidial nature is the intracellular lumen. 

 But in Encliytroius alhidus {v. ant.) the lumen is certainly not 

 intracellular. And in any case there is no fundamental differ- 

 ence between intercellular a.nd intracellular tubes; whether the 

 lumen of any tube is intracellular or not depends on the size of 

 the lumen and the size of the cells of which the tube is composeii. 

 Suppose we start with a tube of fair size, in the cross-section of 

 which several cells are seen to bound the lumen ; if the size of the 

 tube is diminished, fewer cells will serve to surround the cavity. 



