Mr. H. J. Carter on Ploesconia and Keroiia. 2J5 



sent a movement of its bars in succession to that of the wreath 

 of cilia with which it is conjoined anteriorly ; but as this wreath 

 appears to be chiefly concerned in bringing the particles of food 

 to the oral orifice, I am not certain that the gill may not have an 

 independent, perhaps respiratory, function. 



The abdominal cavity at first appears to be equal in extent to 

 the dorsal surface ; but the particles of food never extend to all the 

 margins of the latter, and are seldom seen to occupy more than 

 the anterior and right two-thirds of this space, while opposite the 

 triangular depression leading to the mouth the dorsal and ventral 

 surfaces appear to be nearly in contact, which accounts for the 

 greater transparency of this portion ; however, in fig. 2, where the 

 embryonic cells well mark the extent of the abdominal cavity, a few 

 of them may be seen over the lower part of the gill, and extend- 

 ing forwards on the left side of the triangular depression. This 

 area has been coloured with a dark shade in fig. 3 a, in oi'der to 

 show in relief the gill and part of the ventral surface by which 

 it is bordered. I question, too, whether the under lip (fig. 2 a) 

 is not more prominent in the representations generally than 

 it is in nature, and also think that this may be owing to the 

 pressure of the covering slip of glass. The contracting vesicle is 

 surrounded by several sinuses, which, filling first, then pour their 

 contents into it, while these again appear to be expelled by the 

 contracting vesicle through the anal orifice — assuming that the 

 anal orifice in P. iruncata is situated in the same position as in 

 the following species. I have never been able to discover any 

 hepatic cells (viz. those containing cellules or oil-globules), in the 

 abdominal cavity of either Ploesconia or Keruna, such as those in 

 Nassula, &c., and nothing but a number of refractive globules, 

 which appear to be of an oleaginous composition, and secreted 

 direct from the sarcode. We have the same differences in the 

 common worm Nais and in the microscopic Filaria ; viz. the 

 hepatic element in the former consists of cells which produce 

 the oil-globules, and the oil-globules in the latter are produced 

 apparently independent of cells. 



Of the position and shape of the nucleus, too, in P. truncata, 

 I am not quite certain ; for I have only been able to see it once, 

 in apparently half-starved individuals, and then it was so in- 

 distinctly marked, that, without further confirmation, I cannot 

 assert that it is truly represented in fig. 4. I doubt if it ever 

 becomes visible unless the abdominal cavity be void of food, 

 and nearly free from the presence of the hepatic oil-globules and 

 granular matter, as it was in this instance. 



It will now be obvious that the terms " hooks'' and " horns," 

 originally applied to the legs of the Ploesconia', are calculated to 

 mislead, as the hook-like appearance merely arises from the bent 



