422 Dr. O^Bryen Bellingham on Irish Entozoa. 



XLVII. — Catalogue of Irish Entozoa^ with ohservatioris. By 

 O'Bryen Bellingham, M.D., Fellow of and Professor of 

 Botany to the Royal College of Surgeons in Ireland, Member 

 of the Royal Zoological, Geological and Natural History So- 

 cieties of Dublin, &c. 



[Continued from p. 340.] 



Genus 12. Distoma. 



(Derived from lis, bis, and oro/xa, as.) 



Body soft, flattened, sometimes nearly or quite cylindrical, without 

 articulations, provided with two more or less circular pores or ori- 

 fices ; one of which is anterior and terminal, the other ventral. 



The genus Distoma was established by Linnaeus under the name 

 ofFasciola ; this was adopted by Miiller andGmehn : subsequently 

 it was changed to Planaria by Goetze ; but the term Distomaj pro- 

 posed by Retzius, is now universally adopted. The genus Distoma 

 contains a very large number of species, 162 being enumerated 

 by Rudolphi in his ^ Synopsis,^ of which 39 are doubtful. They 

 are more common in fish and birds than in any other class of 

 animals, and they usually inhabit the alimentary canal. 



The anterior pore in the genus Distoma is subservient to the 

 process of nutrition ; the digestive apparatus commences at it and 

 soon divides into two canals, which pass backwards, running 

 parallel to one another, near the centre of the body, towards the 

 caudal extremity, where they terminate. The ventral pore is sub- 

 servient to the process of generation ; the organs of reproduction 

 consist of ovaries, convoluted spermatic tubes, a receptacle (con- 

 sidered from analogy to be a uterus), and a penis. The ovaries 

 are much branched, occupy the circumference of the body, uniting 

 upon each side into two principal trunks, which communicate with 

 one another, and terminate in a receptacle, from which a slender 

 tube leads to the ventral orifice. The penis is often seen projecting 

 a little in front of this orifice. There is said to be no anal orifice, 

 but upon several occasions I have seen what appeared to be an 

 orifice, terminating the caudal extremity. 



The species of the genus Distoma being numerous, and often 

 of minute size, are in many cases vrith difficulty distinguished 

 from one another. They have been arranged by Rudolphi in two 

 divisions : in one the head, neck, or body is armed with minute 

 spines ; in the second these parts are naked or unarmed. They 

 are further subdivided as the body is flattened or cylindrical ; and 

 again, as the anterior or the ventral pore is the larger. The latter 

 is perhaps an unfortunate character upon which to found specific 

 distinctions, as the size of the pores varies when the animal is alive^ 

 and may have somewhat a different shape then from what it has 



