2 LaidlAW, Classification of the Poly clad Tiirbellaria. 



Acotylea where a vagina of this type occurs, it is usually 

 of nearly equal calibre throughout, and the shell-glands 

 lie along a considerable part of its length, instead of being 

 grouped about one level. Cestoplana, however, amongst 

 the Acotylea, rather recalls the Cotylean condition of the 

 shell-glands. Any accessory organs, whether vesicular or 

 glandular, which may occur in connection with this type 

 of vagina are, I believe, invariably developed on the 

 uteri. 



All Cotylea are provided with a vagina of the first 

 type, and also certain Acotylean genera : such are 



Alloioplana, 

 Cestoplana, 

 Stylochus, 

 Hoploplana, 

 etc., etc. 



Certain species also, belonging to genera in the 

 majority of whose species the second type of vagina 

 occurs, possess a vagina of this first type. Such a species 

 is Stylochoplana nationalis v. Plehn ('96a). 



The second type of vagina is confined to the 

 Acotylea, though not found universally in that group. 

 Here the vagina, after receiving the openings of the two 

 uteri (which almost invariably combine just before they 

 enter the vagina to form a short, median, common duct) is 

 continued back to form what is spoken of as the accessory 

 part of the vagina. This accessory part may be simply a 

 vesicle opening into the vagina immediately behind the 

 uterine opening, or it may be divided into two parts, viz. : — 

 a long duct-like part which opens at its (morphologically) 

 hinder end into a vesicular part ; this vesicular part is 

 usually median, but in some cases it is practically bi- 

 laterally symmetrical, of a crescentic shape with its horns 

 directed forward, as for example in Discocelis tigrina. 



