PROTEOLEPAS BIVINCTA. 595 



the eighth segment, the whole muscular system would have 

 been perfectly symmetrical. The oblique latero-ventral 

 muscle in the sixth segment is distinctly striated trans- 

 versely; but this is not the case with most of the other mus- 

 cles, if with any of them ; I cannot account for this difference. 

 The muscles of the gnathites are the only other voluntary 

 muscles in the animal's body. 



Homologies of the Body. — It will hereafter be, I think, 

 clearly shown, that when the shell and integuments of the 

 pupa of Proteolepas are shed, no carapace or general covering 

 for the body is formed ; the three anterior segments of the 

 head, the backward prolongation of which (as has been else- 

 where explained) certainly forms the carapace of ordinary 

 cirripedes, being here almost absolutely aborted. In every 

 cirripede the mouth is formed of three pairs of gnathites, 

 which, no one will doubt, rise from the fourth, fifth, and 

 sixth segments of the head : here in Proteolepas, the mouth, 

 even on the view of the mandibular organ on each side being 

 compounded of only two gnathites, sufficiently resembles the 

 ordinary cirripedial type to make it very probable, that if 

 examined in the earliest stage of its development, three pairs 

 of gnathites would be discovered. In accordance with this 

 conclusion, the segment succeeding the mouth (i. e., the first 

 segment of the body in fig. 7) homologically is the seventh, 

 or last cephalic segment. The succeeding seven segments, 

 of course, are the seven thoracic segments, and the three 

 posterior segments are abdominal ; the latter are not deve- 

 loped in ordinary cirripedes when mature, but are present 

 during their pupal condition. Now this conclusion, which 

 is, in fact, deduced from what we know of the front part of 

 the head in other cirripedes, both larval and mature, appears 

 to me most satisfactorily confirmed by the differences in the 

 muscular system of the segments in Proteolepas. In no 

 other way, I believe, can it be explained, why the last cephalic 

 segment and the three abdominal segments should differ 

 from the seven thoracic segments, in the entire absence of 

 the oblique lateral muscles. The abdominal segments, 

 moreover, differ a little in shape, in the indistinctness of their 

 articulations, in the thinness of the longitudinal muscles, and 

 even in their contents. With respect to the two threads 



