566 THE AMERICAN NATURALIST. [Vor. XXXV. 
in the eighteenth abnormal somite (Fig. 3). At this point 
the ventral longitudinal muscles and nerve cord of the abnor- 
mal side have disappeared, and the parapodia s.’ and dr. are in 
close proximity, their inferior ligula nearly touching each other. 
They are now noticeably smaller than in Fig. 2 ; s. and dx., on 
the other hand, have remained constant in size, but s., no longer 
projecting ventrally, has swung around into a more lateral 
position on the left side of the median plane. As a result, the 
ventral surface of the animal is now more nearly parallel to the 
dorsal surface. Except for the absence of ventral cirri, s.’ and 
dx.’ still possess all their normal parts, but the relative size of 
mul. cdn. va. v. 
i eS 
\ Se 
1 
abnormal somite and its 
ium; dx.', right abnor- 
Fic. 3. — View of the anterior face of a section through the eighteenth 
ormal para 
^, left 
appendages. (X 6.) cd.n., nerve cord; dx., right n 
mal parapodium ; zz4.7., longitudinal ventral muscles ; s., left normal parapodium; s. 
abnormal parapodium ; va.v., ventral blood vessel. 
these parts is such as is characteristic of parapodia which are 
in process of development, rather than ot fully formed append- 
ages. This condition of arrested development is most notice- 
able in the ligulz of the dorsal rami, which are disproportion- 
ately small as compared with those of the normal appendages 
of this metamere. : 
Tracing this same series of appendages (s. and dx.) back 
into the twenty-first abnormal somite (Fig. 4), they appear still 
further reduced. In appendage dr.’ the dorsal ramus is sma" 
and its inferior ligula is wanting. The ventral ramus is appar- 
ently represented by only the inferior ligula and aciculum. 
Appendage s.' is even more rudimentary, being represented by 
