G32 ANNELIDA I — TOMOPTERIS. 



492. Among other animals captured by the Tow-Net, the Marine 

 Zoologist will be not unlikely to meet with an Annelid which, 

 although by no means Microscopic in its dimensions, is an admi- 

 rable subject for Microscopic observation from the extreme trans- 

 parence of its entire body, which is such as to render it difficult to 

 be distinguished when swimming in a glass jar, except by a very 

 favourable light. This is the Tomopleris, so named 'from the divi- 

 sion of the lateral portions of its body into a succession of Wing- 

 like Segments (Plate xxiii., b), each of them carrying at its ex- 

 tremity a pair of Pinnules, by the movements of which the animal 

 is rapidly propelled through the water. The full-grown animal, 

 which measures nearly an inch in length, has first a curious pair 

 of ' Frontal Horns ' projecting laterally from the Head, so as to 

 give the animal the appearance of a Hammer-headed Shark ; be- 

 hind these there is a pair of very long Antennae, in each of which 

 we distinguish a rigid bristle-like stem or Seta, enclosed in a soft 

 sheath, and moved at its base by a set of Muscles contained within 

 the lateral protuberances of 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 less- 

 ening in size until they become almost rudimentary ; and where 

 these cease, the body is continued onwards into a Tail-like pro- 

 longation, 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 con- 

 tinued 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 antennas, a Ganglionic mass, the component cells 

 of which may be clearly distinguished under a sufficient magnify- 

 ing power, as shown at f ; seated upon this are two Pigment-spots 

 (b, b), each bearing a double pellucid Lens-like body, which obvi- 

 ously have the character of rudimentary Eyes : whilst imbedded 

 in its anterior portion 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 (Esophagus 

 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 appen- 

 dage, however, it is always narrowed into an Intestinal canal ; 

 this, when the appendage is in 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 parts of the 



