TOMOPTEEIS 



953 



ance of a ' hammer-headed ' shark ; behind these there is a pair of 

 very long antennae, in each of which we distinguish a rigid bristle- 

 like stem or seta, inclosed in a soft sheath, and moved at its base 

 by a set of muscles contained within the lateral protuberances at 

 the head. Behind these are about sixteen pairs of the ordinary 

 pinnulated segments, of which the hinder ones are much smaller 

 than those in front, gradually lessening in size until they become 

 almost rudimentary ; and where these cease the body is continued 

 onwards into a tail-like prolongation, the length of which varies 

 greatly according as it is contracted or extended. This prolongation, 

 however, bears four or five pairs of very minute appendages, and 

 the intestine is continued to its very extremity, so that it is really 

 to be regarded as a continuation of the body. In the head we find, 

 between the origins of the antennae, a ganglionic mass, the component 

 cells of which may lie clearly distinguished under a sufficient mag- 

 nifying power, as shown at F ; seated upon this are two pigment- 

 spots (b, b), each bearing a double pellucid lens-like body, which are 

 obviously rudimentary eyes ; whilst imbedded in its anterior por- 

 tion are two peculiar nucleated vesicles, a, a, which are probably 

 the rudiments of some other sensory organs. On the under side of 

 the head is situated the mouth, which, like that of many other 

 Annelids, is furnished with a sort of proboscis that can be either 

 projected or drawn in ; a short oesophagus leads to an elongated 

 stomach., which, when distended with fluid, occupies the whole 

 cavity of the central portion of the body, as shown in fig. B, but 

 which is sometimes so empty and contracted as to be like a mere 

 cord, as shown in fig. C. In the caudal appendage, however, it is 

 always narrowed into an intestinal canal ; this, when the appendage 

 is in an extended state, as at C, is nearly straight ; but when the 

 appendage is contracted, as seen at B, it is thrown into convolutions. 

 The perivisceral cavity is occupied by fluid, in which some minute 

 corpuscles may be distinguished ; and these are kept in motion by 

 cilia which clothe some parts of the outer surface of the alimentary 

 canal and line some part of the wall of the body. K"o other more 

 special apparatus, either for the circulation or for the aeration of 

 the nutrient fluid, exists in this curious worm, unless we are to 

 regard as subservient to the respiratory function the ciliated canal 

 which may be observed in each of the lateral appendages except 

 the five anterior pairs. This canal commences by two orifices at 

 the base of the segment, as shown at fig. E, b, arid on a larger scale 

 at fig. D ; each of these orifices (D, , b) is surrounded by a sort of 

 rosette, and the rosette of the larger one () is furnished with 

 radiating ciliated ridges. The two branches incline towards each 

 other, and unite into a single canal that runs along for some dis- 

 tance in the wall of the body, and then terminates in the perivisceral 

 cavity, and the direction of the motion of the cilia which line it is 

 from without inwards. 



The reproduction and developmental history of this Annelid 

 present many points of great interest. The sexes appeal- to be 

 distinct, ova being found in some individuals and spermatozoa in 

 others. The development of the ova commences in certain ' germ- 



