918 REPOET OF COMMISSIONER OF FISH AND FISHERIES. [40] 



certainly also be glandular and be no exception to the rule, and the 

 difference should then only refer to the form or perhaps pellucidity of 

 the organ. According to Vejdovsky, who calls this organ " kittgange," 

 anything similar should not be found anywhere else, not even in Lim- 

 nodrilus, and would in such a case, together with the globular chamber 

 form an accessory organ entirely distinct from the atrium. I am satis- 

 fied, however, that this is not the case, and think that the two parts 

 just referred to, the circular chamber and the pellucid tube, constitute 

 nothing else than the atrium proper. And that part to which Vej- 

 dovsky has given the name of atrium proper is evidently nothing else 

 than the upper part of the penis proper. When we in all the other 

 species of Tnbificidce assign the name of atrium to that part of the effer- 

 ent duct which supports the prostate gland, why should we give it an- 

 other name in Psammoryctes only because it here has a somewhat dif- 

 ferent form? Is it not easier to imagine that an old organ has been 

 modified than to believe that a new one has been added ? 



In HemituUfex we meet with an atrium of somewhat similar shape. 

 The upper end of the same, close to the efferent duct proper, is also 

 globular and supports the prostate gland, and is, as far as I can judge 

 from figures and descriptions, entirely homologous to the same organ of 

 Psammoryctes. The narrower part of the atrium, however, is not quite 

 so regular and tube-like as in this latter genus, but the homology of the 

 organs seems evident. Also, in RemituUfex this lower part of the 

 atrium is less glandular than the circular chamber, but this is also the 

 case in nearly all the species I have investigated and is not characteris- 

 tic of the genus. That part of the organ which corresponds with what 

 Vejdovsky calls "«^n«<m" is, at least in HemituUfex, nothing else than 

 the upper part of the penis proper. 



The figures will in every instance give a better idea of the organs in 

 question, and I must therefore mainly refer to them. (For Hemitubifex 

 see PI. VII, Fig. 6 c.) 



In Tubijicini we find the atrium furnished with only one single-lobed 

 prostate gland, the form of which only varies little in the different 

 species. It always takes the shape of a more or less sponge-like, or 

 even fan-shaped, body, the latter when seen in optical section. The 

 size of the cells composing the prostate varies in different species, but 

 not enough to furnish species characteristics. 



If we now turn to the last remaining part of the copulative organ, 

 the peuis proper, we will find it of considerably different form in the 

 different species. The most common form of the penis is that of a long, 

 narrow cylinder, tapering towards its exterior apex. The exterior apex 

 of the penis is either rounded, as in Camptodrilus and certain species of 

 Limnodrilus, or truncate, as in Limnodrilus monticola. In Limnodrilus 

 Steigenvaldii the apex of the penis is considerably swelled j in Limno- 

 drilus Silvani the penis is swelled above the apex. In Hemitubifex and 

 Psammoryctes the upper end of the penis is considerably enlarged above 



