268 



another following the course of the post-oral tentacles and lastly a 

 peri-anal ring. 



Thus the ciliated areas practically consist of a pre-oral ring (par- 

 tial) and two post -oral rings, corresponding to the three segments of 

 the body (pre-oral, collar, and trunk). 



It is impossible in a short note to follow up these and other points 

 to their logical conclusion, but it is well to compare Actinotrocha with 

 Tornarla in their leading characters. 



The following features are common to each: — 



1) A bilaterally symmetrical triploblastic pelagic larva. 



2) A complete and functional alimentary canal, a ventral mouth, 

 short oesophagus, stomach and hind-gut (intestine), a terminal anus. 



3) A large pre-oral lobe covering over the mouth. 



4) Three ciliated bands, more or less sinuous — the first or pre- 

 oral encircling (partially or wholly) the pre-oral lobe — the second or 

 post-oral encircling the area immediately behind the mouth and often 

 following the course of a number of tentacles, into which this region 

 of the body is produced — the third or peri-anal, usually simple and 

 encircling the hind part of the body. (In Tornarla the pre-oral ring 

 very nearly meets the post-oral, in the mid-dorsal line.) 



5) A thickened apical plate on the dorsal surface of the pre-oral 

 lobe, bearing in most cases, a pair of eye spots. 



6) Mesoblast consisting mostly of an unpaired coelomic sac in the 

 pre-oral lobe and two pairs of post-oral coelomic sacs, the sacs are 

 mostly separated by mesenteries but the dorsal one may be absent. 



This list will be quite sufficient to shew the very close agreement 

 in structure between the two larvae. 



Some extremely important generalisations follow from the above 

 facts but these must be left to the complete paper which will, I hope, 

 shortly be published. I think Phoronis will either have to te placed 

 in the Hemichordata or will have to constitute a group Diplo- 

 chordata having the same relation to Balanoglossus as ürochor- 

 data to Amphioxus. 



United College, St. Andrews N.B., April 6. 1896. 



5. Diploposthe, eine neue Gattung von Vogeltaenien. 



Von Dr. Arnold Jacob i in Leipzig. 



eingeg. 13. April 1896. 



Diejenigen Formen unter den Cestoden, welche mit doppeltem 

 Geschlechtsapparat versehen sind, haben besonders in neuerer Zeit 

 eine generische Sonderung von ihren Verwandten erfahren; eine 



