1876.] 23 [Minot. 



to draw attention to this point. There are two vaginae in Polystomum - 1 

 Concerning the water vascular system there exists much doubt; I 

 have treated this point elsewhere. I have finally to mention peculiar 

 cords of parenchymatous tissue that run lengthwise through the body 

 of numerous Plathelminths. These were first noticed by Sommer and 

 Landois in Botriocephalus, then by Mosely in the Land planarians, 

 and by Salensky in Amphilina, and were considered by all these au- 

 thors to be part of the water vascular system. Nitsche 2 showed that 

 it could not be, because the cords (Balkenstraenge) exist in Taenia 

 beside the true water vascular system. I have been unable to de- 

 termine what these structures really are, although I have met with 

 them in a variety of Planarians. They are what Schneider took for 

 nerves in Ligula. 



It appears from the above account that the Plathelminths are all 

 closely related, so far as we can judge from the structure of the aduifc 

 forms. I have never investigated the development of the class. 



The Trematods and Cestods agree with one another and differ 

 from the other members of the class in having a vagina, a simple 

 muscular system, and digestive apparatus, a very simple ganglion or 

 none at all; presenting, in short, reduction of all those organs that 

 are unessential to parasitic life. I propose, therefore, to unite them 

 under the name of Vaginiferae. The union of the two orders is 

 rendered still more natural because there is a gradual passage from 

 the segmented Cestods to the ordinary Trematods. This passage is 

 formed by Taenia, Botriocephalus, Triaenophorus, Ligula, Caryophyl- 

 laeus, Amphilina, Distomum. Similarly the Dendroeoela must be 

 united with all those Rhabdoccela that have a proboscis. For this 

 group I propose the name Pharyngocoela, which has already been 

 used by Prof. Leuckart in his Jahresberichten. The remaining Rhab- 

 docoela may be classified in the way proposed by Ulianin 3 in two 

 groups, Apliaryngea and Accela. 



1 Zeller. Weiterer Beitrag zur Kenntniss des Polystomum. Zeit. wiss. Zool. Bd. 

 xxvn (Heft 2, 1876), p. 238. 



J Untersuchungen iiber den Bau der Taenien. Ibid., xxiii, p. 195. 



8 Ulianin. Die Strudelwlirraer des Sebastopolischen Hafens. Moskau, 1870. Ver- 

 hand. zweiten Natforsch. Versamm. in Moskau (in Russian). 



