12 ART. 11. — A. IZUKA : OBSERVATIONS ON THE 



about the tenth, they increase in size gradually and successively, 

 along with the increase in breadth of the body in that region. 

 Then they keep up approximately the same size for some distance 

 further backwards ; and in the hind region of the body, they 

 again become gradually smaller and smaller, until the very last 

 parapodium, occurring in the prseanal segment, is represented by 

 quite a simple and insignificant elevation. To illustrate in a way 

 the variation above indicated, I have shown in the Woodcuts 1- 

 4 (p. 10) respectively the 1st, 10th, 30th and 160th parapodia, 

 taken from an average-sized individual with 178 segments. 



In the first parapodium (Woodcut 1) the superior ramus is 

 always entirely destitute of the acicula and the bristles, and is 

 simply provided with the dorsal cirrus and the ligula. The 

 former is well developed, being about twice as long as the latter. 

 Its basal section, making up about one-fifth of the entire length, 

 is marked off by constrictions from both the distal section and 

 the ramus bearing it. The ligula is small and simple in ap- 

 pearance, and has a rounded tip. In the much more complicated 

 inferior ramus the two terminal lobes are of about the same size. 

 The upper lobe projects slightly farther out than the ligula, while 

 the lower is directed outwards and downwards. The ventral 

 cirrus is nearly similar in shape and size to the dorsal, but 

 differs in having no basal section marked oil'. The ventral acicula 

 present and the bunches of bristles occuring in association with 

 it are rather weakly developed. 



Generally speaking the second parapodium and sometimes 

 even the third are essentially like the first, the dorsal ramus 

 being characterized by the absence of both the acicula and the 

 bristles. 



The next parapodium — that is, generally the third, but 



