M. H. de Lacaze-Datliiers on Phoenlcuvus. 161 



Tlie last organ of which I was able to ascertahi the exist- 

 ence is a very simple gland formed by a tube terminating in 

 one or two C£eca, and bearing some rare lateral caeca. One 

 of them, directed towards the white surface of the body, but 

 not extending to the integuments, is constant and larger. 

 This gland is situated towards the marbled surface, and opens 

 into the buccal orifice itself. What are its functions ? It is 

 difficult to say, although it seems natural to regard it as a 

 salivary gland. 



I have proved that what Delle Chiaje regarded in Tethys 

 as an aquiferous apparatus was nothing but the venous appa- 

 ratus of the mollusk, opening externally at the apex of the 

 papilla situated in the centre of the interbranchial fossse. 

 The Phoenicurus^ grasping this papilla with its mouth, can 

 therefore at any moment suck in the sanguine fluid of the 

 TethySj of which it is the parasite in the most exact accepta- 

 tion of the word. 



From what has been stated it is now easy to place and 

 orientate the animal. Placing the nervous system posteriorly, 

 the white surface evidently represents the back, and the 

 marbled surface is anterior ; the mouth being placed above, 

 all the positions are easy to characterize and indicate. Hence 

 to find the nervous system we must open the Phoenicurus at the 

 back, and remove the subcutaneous tissues, and it is in front 

 of the muscular bands that we discover the ganglia ; then it 

 will be seen that in passing from back to front we find the 

 nervous system, the digestive tube, and the salivary gland. 



Phoenicurus appears to me to be very distinctly characterized 

 as a Dendrocoelan by the absence of the abdom.inal ganglionic 

 chain and by the arrangement of its arborescent intestine. 



To fix more completely its zoological relations it would be 

 of service to have traced its evolution. Now, in the month of 

 May, 1 was unable to discover the organs of reproduction j 

 only once I found an individual in which the large cells above 

 mentioned had acquired enormous proportions. The skin of 

 the animal being torn, they projected outwards like bunches 

 of grapes. I will not assert that they represented ova, for all 

 questions relating to reproduction remain to be cleared up. 

 It is important that I should repeat that my observations were 

 made in the month of May, and tliat^ in the animals preserved, 

 I have not met with reproductive organs, which are so easily 

 recognized in the Turbellaria or the Trematoda. 



Does Phoenicurus represent only a period or a stage of its 

 whole existence? Is it a creature deformed or degraded by 

 parasitism ? Is its evolution accomplished under varied forms 



