ANNULOSA, OR WORMS. 201 



about sixteen pairs of the ordinary pinnnlated 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 pro- 

 longation, 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 antennas, a ganglionic mass, the component cells of 

 which may be clearly distinguished under a sufficient magnifying power, 

 as shown at F; seated upon this arc two pigment-spots (b, b), each bear- 

 ing a double pellucid lens-like body, which are obviously rudimentary 

 eyes: whilst imbedded in its anterior portion are two peculiar nucleated 

 vesicles, #, , 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 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. No 

 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 

 shovm at fig. E, Z>, and 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 (a) is furnished with radiating ciliated ridges. The two branches 

 incline towards each other, and unite into a single canal, that runs along 

 for some distance in tho 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. 



598. The Reproduction and Developmental history of this Annelid 

 present many points of great interest. The sexes appear to be distinct, 

 ova being found in some individuals, and spermatozoa in others. The 

 development of the ova commences in certain ' germ-cells ' situated within 

 the extremities of the pinnulated segments, where they project inwards 

 from the wall of the body; these, when set free, float in the fluid of the 

 perivisceral cavity, and multiply themselves by self-division; and it is 

 only after their number has thus been considerably augmented, that they 

 begin to increase in size and to assume the characteristic appearance of 

 ova. In this stage they usually fill the perivisceral cavity not only of the 

 body, but of its caudal extension, as shown at c; and they escape from it 

 through transverse fissures which form in the outer wall of the body, at 

 the third and fourth segments. The male reproductive organs, on the 

 other hand, are limited to the caudal prolongation, where the sperm-cells 

 are developed within the pinnulated appendages, as the germ-cells of the 



