liejiroductice Organs of Vitriiia, 399 



if \ Last spire augulated anyulusa. 



j Last spire not angulaled , . . . . 3 



q i A columella 4 



( No columella 5 



. j Shell lielicoid, globular lyelugka. 



\ Shell slightly globular; the last spire elongated laxata. 



r \ Shell globular, resembling a young Helix mollis. 



^ ) Shell depressed G 



I Three spires in the shell, " idtlnivs macimis " brumalis. 



\ Two and a half spires in the shell , " tdtiums permagnas ". . hrevisjjira. 



The asexual Vitrime belong to sections 5 and 6, and are 

 nearly allied to mollis, brumalisj and hrevisjyira. The three 

 species recorded from St. Michael's are laxata, hrumalis, and 

 hrevisjnra ; and we should therefore expect that the asexual 

 mollusks, if really hybrids, would be the offspring of brumalis 

 and hrevispira. At first sight, however, they resemble most 

 closely neitiier of these, but mollis, a species hitherto unknown 

 in the island. It is, of course, possible that mollis occurs 

 there but has been overlooked. I have not been able to find 

 any sexual Vitrina in the neighbourhood of Ledo, except 

 brumalis. 



Quite recently I have revisited the spot expressly to search 

 for more neuters ; but the search was unproductive. 

 Ponta Delgada, July lo, 1881. 



T have dissected two of the three Vitrince sent over by Mr. 

 Furtado, without finding any trace of reproductive organs. 

 The parts are usually very voluminous in snails, and it is not 

 easy to make a mistake as to their presence in a normally 

 developed animal. In order to investigate the point more 

 carefully, the third speciiuen "was cut into transparent slices 

 and compared microscopically with similar sections of Helix 

 aspersa ; but no reproductive organs were found. The multi- 

 tude of details revealed by the microscope makes it difficult to 

 speak confidently as to the complete absence of any structure 

 which is not recognized ; and I rely upon the simple dissec- 

 tions more fully than upon the microscopic examination. 



Abortion of the reproductive organs has been observed in 

 animals infested by parasites, e. g. in stylopized bees, in 

 Lymncea stagnalis when attacked by Trematodes, and in 

 female hermit-crabs attacked by Khizocephala. The complete 

 abortion of the parts in the remarkable case described by Mr. 

 Furtado distinguishes it at once from the many cases of real 

 or supposed functional defect met with in hybrids. — L. G. M. 



