326 iS. I. Sjnith — Early Stages of Hippa talpoida. 



the non-calciiied integument ; but when the antenna is folded away 

 within the external maxillipeds, the rod is transverse to its former 

 position and is almost or quite hidden between the second and fourth 

 segments, the outer, calcified portion of the latter segment folding 

 over the previously exposed area of thin integument. The flagellum 

 is stout, tapers very gradually to an obtuse and rather thick tip, and 

 is composed of about twenty-five segments, which are very short 

 proximally, but increase regularly in length distally until, near the 

 tip, they are longer than broad. Each segment is armed upon One 

 side with a fascicle of long, pectinated setae. As seen in a transverse 

 section of the flagellvmi (Plate XLV, fig. 6), the outer one of these 

 setse, on each side of the fascicle, is strongly curved inward at the 

 extremity and much longer than the inner ones, which are nearly 

 straight and armed, for only a part of their length, with much shorter, 

 strono-er, flattened, and blade-shaped teeth. In this stage there are 

 usually from five to seven setae to each segment, the median one or 

 two often being simply aciciilar, or even very small and rudimentary. 

 This structure of the flagellum of the antenna is essentially the 

 same as in the adult, where, however, the number and size of the 

 satae, as well as the extent of their armament, is enormously increased 

 upon each segment, Avhile the number of segments is several times 

 greater than in the megalops-stage. In the ordinary adult specimens, 

 there are one hundred to one hundred and fifty segments in the 

 flagellum and eight to twelve setae to each segment. There are two 

 forms of these setie in each fascicle, as in the megalops-stage. The 

 outer one, each side of every fascicle, is very long and convolutely 

 curved inward at the extremity ; while all the others are shorter, 

 thouo-h varying much in lengtli among themselves, and nearly 

 straio"ht. The long, outer setae are armed, for nearly their whole 

 length, with very long, almost filiform, secondary setae, which are 

 arrano-ed in a double series along the inner side of the curve. These 

 secondary setae are exceedingly slender, very slightly tapering, from 

 •2 to -25™"' loiig? — the longer ones being on the distal half though not 

 at the extremity, — and are placed ' so thickly that, in the middle 

 portion of the seta, there are two hundred in the space of a millimeter. 

 The extremity of the shaft of the seta itself is unarmed for a very 

 short distance, curved sharply so as to be nearly parallel, with the last 

 of the secondary setae, and tapers to a very slender and acute tip. 

 The remaining setae of each fascicle are nearly straight, or very 

 slif>'htlv bent, and armed upon the outside of the curve. The teeth, 

 as in the outer setae, are arranged in two series, which here, however, 



