134 Proceedings of the Royal Society of Victoria. 



work may overlap that of Mr. Rousselet. Having arrived at a 

 similar conclusion with regard to the undulating membrane 

 before knowing his view and having figured a similar structure in 

 five species it will corroborate this portion of his observations and 

 extend it to other families. The two flagella on the outside of 

 the tag as mentioned by him were undoubtedly present. It does 

 not, however, appear to be necessary to assume that the spongy 

 looking protoplasmic cap permits the passage of fluid from the 

 body cavity into the tag as he suggests. Rather are not the 

 thin walls instrumental in passing by osmosis the excretory fluids. 

 From this point of view the fan-like expansion of the tag is to 

 be explained as affording a larger surface area. Comparing the 

 areas available for this, taking the narrow line of the caps on the 

 one hand and the two flat sides on the other in Asplanchnopus 

 inyrrneleo, we should get, taking the thickness of the tag as 4th 

 of its breadth and other dimensions as measured, areas in the 

 pi'oportion of about 11 to 1. That the fluid excreted is con- 

 siderable is shown by the fact that in A. myrmeieo the contractile 

 vesicle when expanded occupies about ith of the body cavity and 

 contracts at intervals of a few seconds. I counted 50 tags on 

 one side making 100 in all. Assuming that the fluid passes 

 through the sides, the organ in this view become an admirably 

 adapted force pump to drive the fluid into the canals, the swing 

 causing the crests of the undulations in the membrane to come in 

 contact with the wall on either side. Further if flagella are in 

 action internally they would be required to propel the fluid in the 

 direction of their free ends, whereas in the collared and other 

 Protozoa the action of the flagellum is to cause a current inward 

 to the base. 



Of the forms examined I refer to the accompanying figures 

 without further comment excepting those of the tags of A. 

 7nyrmeleo which liave not to my knowledge been described. 

 There are also some additional features of interest. Fig. 9 is a 

 portion of a canal with tags at {a), {b) and (c) in narrow aspect 

 and (d) in the flat. In this form there is one external flagellum 

 about as long as the whole cell seen in the middle from the flat 

 view and to one side side in the narrow aspect. Some cells, one 

 shown in two aspects in fig. 12 and 13 attached to the convoluted 

 portion of the duct at the posterior of the animal appear destitute 



