104 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [398] 



ularly interesting on account of its remarkable mode of reproduction, 

 for, like several other marine annelids, it presents the phenomena of al- 

 ternate generation. Its history has been well given by Mr. A. Agassiz.* 

 The very numerous eggs of the female (fig. 66, e) are at first contained in 

 the general cavity of the body, between the intestine and the outer wall, 

 along the whole length of the body ; afterwards they pass into a pouch 

 on the lower side of the body, extending from the twelfth to about the 

 twenty-sixth segment ; in the pouch they hatch into young worms, and 

 soon after the sac bursts and they escape into the water. The females 

 apparently die after discharging the young. The eggs do not develop 

 into males and females, but into the asexual or neuter individuals, (fig. 

 65,) which differ widely from the others in form and in the eyes and other 

 appendages of the head, as well as in the internal anatomy and lateral 

 appendages. After these neuter individuals become nearly full-grown, 

 having forty to forty-five segments, a median dorsal swelling arises 

 at about the thirteenth or fourteenth segment, most commonly on the 

 thirteenth, and soon after two others arise from the sides of the same 

 segment and develop rapidly; these swellings finally become the three 

 front tentacles of a new head, (a, a, a, fig. 65 ;) soon a pair of eyes appears 

 on the upper side of the segment, than a pair of tentacular cirri ; then 

 the second pair of eyes ; then other appendages of the head, until finally 

 a complete head is formed, having the structure belonging to the head of 

 a male or female, as the case may be. As the new head, with its append- 

 ages, becomes more completely organized, the segments posterior to it, 

 which are to become the body of the new individual, become more highly 

 developed, and the lateral appendages more complicated, those back of 

 the fifth in the male, or the sixth in the female, acquire dorsal fascicles 

 of long setae, and the dorsal cirris becomes longer 5 at the same time 

 some additional segments are developed ; and the ova in the female, or 

 spermatazoa in the male, are formed. Finally the new sexual individ- 

 ual, thus formed out of the posterior segments of the original neuter, 

 breaks its connection and swims off by itself, and becomes a perfectly 

 developed male or female. The head of the female is represented in 

 fig. 66 ; a male individual is represented as developing from an asexual 

 individual in fig. 65. The male can be easily distinguished from the 

 female by the pair of large antennae, which are forked in the male, but 

 simple in the female. Farther details concerning this curious mode of 

 reproduction may be found in the memoir of Mr. Agassiz, together with 

 numerous excellent illustrations, in addition to those here copied. 



Associated with the preceding species a few specimens were found 

 which probably belong to another species of Autolytus. These were quite 

 slender, light-red in color, with paler annulations, but only the asexual 

 individuals were observed. Another species of larger size also occurs 

 among the hydroids, near New Haven, which belongs to Autolytus or 



* On Alternate Generation in Annelids, and the Embryology of Autolytus cornutns; 

 Boston Journal of Natural History, Vol. VII, p. 384, 1863. 



