m'donnell on the electric organ of the skate. 57 



of these families to be trie same as those of the genera. The arrange- 

 ment of the cells constituting the corpus adiposurn, the relative size of 

 the males, and the position of the vulva, will probably, however, be 

 found somewhat variable, and are perhaps characters of not more than 

 generic importance ; in which case the arrangement of the nervous sys- 

 tem, the presence or absence of an oesophagus, the presence of a single 

 or double ovary, and the development of the young, will, with the ab- 

 sence of the anus, remain as the principal family characters. 



I shall endeavour to get some humble bees in the course of this win- 

 ter, in order if possible to determine some of the many points which yet 

 remain to be ascertained ; and I should feel very grateful to any one 

 who would send me even a single specimen of any species of Bombus 

 between the months of December and April. In the meantime, Sphae- 

 rularia still remains, as it was when Diesing wrote the " Systema Hel- 

 niinthurn,'' a "genus inquirendum." 



description of plate i. 



1. Sphceridaria bomhi x 15. A. Small male. 



2. Part of corpus adiposum x 10. 



3. Free end of ovary x 250. 



4. Two young eggs with rachis x 250. 



5. Portion of ovary x 250. 



6. Outline of young x 60. 



7. Outline of male (?) x GO. 



8. Head of male x 60. 



9. Tail of do. do. 



10. Ovary x 



11. Egg, showing the commencement of segmentation, x 250. 



12. Do., in a more advanced stage, x 60. 



13. Young egg, still more advanced, x 250. 



14. Place of union of male and female x 250. a. Part of the body 

 of male. b. Part of skin of female, c. Projection of male fitting into 

 sac-like depression of female. 



VII. — On an Organ ln the Skate which appears to be the homo- 

 logue of the Electrical Organ of the Torpedo. By Robert 

 M'Donnell, M. D., F. E. C. S. I., Lecturer in the Carmichael School 

 of Medicine, Dublin. 



In the eyes of those who look without prejudice on the theory of de- 

 scent with modification, the tracing out of homologies has, in recent 

 times, been invested with a new interest. On this theory, the compa- 

 rative anatomist no longer, in following out the homological relations 

 of parts and organs, pursues an object, captivating, but fruitless, as fas- 

 cinating as the solving of a puzzle, but barren as to general results. 



VOL. I N. H. E. I 



