Anatomical structure of Aspidogaster conchicola. 507 



as well as to the manner of branching of the whole system, and 

 finally the smaller twigs and their endings which he was unable to 

 discover. So far as I can judge Voeltzkow followed the vessels 

 only to the end of the third branching. Zacharias, whose article 

 appeared at the beginning of this year, also devoted his attention to 

 the finer histological structure of the excretory vessels and notwith- 

 standing his methods and good microscope he was unable to pursue 

 the vessels to their termini. 



These results I state to give an idea how difficult it is to trace 

 the finest vessels, and thereby also some tangible conception of the 

 minuteness of their end organs. For some time after undertaking 

 the study of Aspidogaster I also met with no results in determining 

 the presence of funnel organs and in fact thought it possible that 

 this was only another of the ways in which this peculiar animal 

 differed from its related Treraatodes. However the idea of similarity 

 of structure in closely related forms spurred me to a continual search 

 and a month or two before the close of last year I already knew 

 that Aspidogaster was, in this particular, no exception to the list of 

 Trematodes which, by careful examination of living forms, have dis- 

 closed a ciliated end organ to the finest capillaries. The method 

 used and admirably adapted to the study of the excretory system, is 

 described at the beginning of this work. 



In studying this system, only the larger canals can be clearly 

 traced and their structure and position determined from sections. The 

 continuity of the system and the distribution of its smaller vessels 

 can only be followed in the living animal, where, through distension 

 by means of their contained fluid as well as by their continuous ciliary 

 motion, these can be followed to their minutest branches. 



For convenience in description I shall start at the external 

 openings and trace backwards through the fewer and larger vessels, 

 the more numerous smaller vessels and capillaries , to the funnel 

 organs i. e. in the opposite direction to the physiological action. And 

 here at the outset I must take exception to all earlier descriptions for 

 Aspidogaster possesses not a single foramen caudale or porus ex- 

 cretorius but two of them. These are situated at the summit of the 

 backwardly projecting, conically shaped posterior end of the body 

 (Fig. 8, 23, 33) when, as frequently is the case, the animal assumes 

 this form. My attention was first directed to this point in the living, 

 young animal where I saw two funnel-shaped pores pointing inwards 

 with their inner walls thrown into series of furrows that curved 



Zool. Jahrb. IX. Abth. f. Morph. 34 



