916 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [38] 



upper and interior surface of the oviduct, but in this case consisting 

 only of two main longitudinal trunks. Such muscles are found in 

 Tubifex, llyodrilus fragilis, and Ilemitubifex, but not in any species of 

 Limnodrilus or Camptodrilus. 



In Limnodrilus Silvani and Hoffmeisteri we find the oviduct sur- 

 rounded by circular or concentric muscles. In the former species, how- ' 

 ever, they are very few. In the genus Camptodrilus we find the most 

 characteristic feature to be the large spiral muscles surrounding the 

 oviduct. They are of an enormous length, many times longer than the 

 oviduct, around which they wind themselves several times. The ex- 

 terior end of these muscles are attached to the body wall, near to the 

 genital porus, but the interior one to the lower part of the oviduct. 

 We get the best idea of these muscles if we to the blunt end of a lead- 

 pencil attach a number of equal threads and afterwards wind them 

 spirally round the pencil towards the pointed end and from here return 

 towards fhe blunt end again, always winding the threads in the same 

 direction, or towards us. 



In some instances it seems as if the spiral musclCvS were wound round 

 the oviduct several times; in others again as if only twice. 



The work such muscles can perform may be easily understood. The 

 upper end of the plexus is funnel-shaped, and, as it seems, eminently 

 adapted to capture the ova, and when once captured a few successive 

 contractions may suffice to push them towards and through the sexual 

 porus. 



In different species said muscles are found to be of very different size. 

 In C. sinraUs they are so minute and fine that careful searching is nec- 

 essary to detect them ; but in other species, however, their strength and 

 thickness make them easily discernible. The occurrence of such mus- 

 cles is unique, not only in the class of Oligoehceta, but also, as far as I 

 know, in the whole animal kingdom. 



EFFERENT DUCT. 



The efferent duct is less subject to variation than any other part of 

 the copulative organ. 



We distinguish of the same, however, two different types, viz : 



a A short and broad tube, found in the genus llyodrilus, and similar 

 to the same organ of Mesenchytrwus of the family JEnchytrceidce. 



J) A longer and more slender tube, found in all the other genera, and 

 corresponding in form to the same organ of ArcMenchytrceus and Neo- 

 cnchytrceus of the family above referred to. 



In llyodrilus sodalis we find the form intermediate between the two, 

 not quite so broad and short as in the two other species of the genus, 

 but also far from reaching the relative length of the same organs of the 

 other genera of TuMJieidce. In J'elmatodrilus the efferent duct 'is un- 

 usually short, but also correspondingly narrow. 



The inner end of the efferent duct is always furnished with a large 



