902 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [24] 



C ooralUnus has also single oviduct, but the penis sheath is gradually 

 increasing- in size from the middle toward its lower or exterior end. 

 This species is somewhat larger than any other in the genus, and the; 

 integument of its body tougher. 



C californicus has the exterior end^ of the penis sheath suddenly ex- 

 panding and deflected, but the deflection is not plate-like, only trumpet- 

 shaped. The whole organ is also comparatively shorter and thicker than 

 in G. ignetis. The oviduct is single. The copulative organs of this genus 

 are comparatively longer and narrower than those of any other genus, 

 Limnodrilus excepted. 



B.— GEOGEAPHIOAL DISTEIB UTION. 



Our present knowledge of the distribution of the genera and species 

 of Tubificidce is so very limited that any general comparison between 

 the countries and the species inhabiting the same can hardly be ex-j 

 j)ected. Tubificides are as yet known only from Europe and ]S"orth 

 America, but there is every reason to believe that we will find them dis- 

 tributed all over the globe wherever ponds, streams, lakes, or wells can 

 be or are found. I have as yet not seen any permanent water, and 

 hardly any larger temporary ones, where Tubificidce could . not be col- 

 lected. 



The above list of species must by no means be considered as in any 

 way exhaustive ; on the contrary, the few species known can only con- 

 stitute a small portion of what in reality exists, and I feel fully satisfied 

 that hundreds, if not thousands, of species will be found, when the dif'i 

 ferent waters of the continents and islands are thoroughly searched. 



Here, then, will we find a class of animals, as yet hardly investigated 

 and very insufflciently known, which in the near future may furnish a 

 rich supply for the student of natural history. 



The study of the geographical distribution of the species of OUgochcett 

 must also be in the highest degree an interesting one, even more so 

 than the geographical distribution of most other classes of animals^ 

 such as birds, reptiles, and mammalia. While the latter have numer-i 

 ous ways of transportation on land, through air and water, the slowh 

 moving OligocJicetes are mostly confined to the very element in which 

 they live, and outside of which they and their eggs would soon perish; 

 The fauna of terrestrial animals, with their various means of locomo- 

 tion, may have changed many times, while the Oligoclicetes in the earth, 

 relatively secure from enemies and less subject to climatic changes, may 

 have survived for ages. Thus the study of the distribution of th( 

 • OUgochceta, especially the purely terrestrial ones, may not only be oi 

 value in considering the former connection of continents and islands,> 

 but also in the study of the climatic changes they have undergone. So 

 have I, for instance, been led to believe with a reasonable degree of ceri 



