218 AUTOLYTITS PBOLIFER. 



throughout the year continuously, Nature has therefore provided for any losses the 

 species may encounter in its varied life-history. 



The buds ( $ and ? ) are found in the pelagic condition all along the shores of 

 Britain, from Shetland to the Channel Islands. Well-developed forms are met with 

 every month, and the younger examples, as might be expected, are equally distributed 

 over the year. 



Habits. — The female buds with the ventral sac (Plate XLIX, fig. 7) are truly pelagic, 

 and are frequently caught in the large mid- water net. So far as the records and specimens 

 of those captured by the tow-nets (and those chiefly the bottom tow-nets) go, the majority 

 occur in February, though a considerable proportion are found in March and April. An 

 occasional form appears every month from June till November. The greatest number, 

 however, are procured in the months first mentioned. From the nature of their origin 

 there is little difference in size between those obtained in February and those in October 

 and November, and the continuance of schizogamy throughout this extended period is 

 noteworthy. 1 



In glancing at a series captured in the tow-net near the bottom, for example, on 

 April 20th, the diversity in size of the ovigerous females is interesting, for they range 

 from 2*5 mm. to about 14 mm. The small forms carry a small mass of ova, the larger a 

 great mass, and there is a marked difference in the size of the ova in these respectively. 

 Thus, on the date mentioned, those of the small mass attached to the small example 

 measured '07 mm., whilst those of the larger were *15 mm. The respective larvse 

 probably show the same disparity, and those from the larger eggs thus might be supposed 

 to enter life with a better chance of survival. That, however, does not necessarily follow, 

 for the smaller may be more inconspicuous. 



After the escape of the larvas the body of the female is diaphanous, and the 

 ovigerous membrane forms soft wrinkled folds at each side. It is probably a cuticular 

 structure, augmented by a secretion of the dermal cells, as in the instance of the tube, 

 and in communication with the body-cavity of the annelid. They probably break up 

 and disappear soon afterwards. . The fine elastic ovigerous membrane keeps the eggs 

 in situ during the active pelagic life of the animal. 



The head of Saeconereis (the female bud) is rounded in front, comparatively small, 

 and with a pair of large connate eyes, situated at the outer and posterior border of the 

 head. The upper part of the pigment looks dorsally and externally, the lower commands 

 the ventral surface as a large dark brown eye on each side, and more conspicuous than 

 the dorsal pair. Each is provided with a lens. A long median tentacle occurs behind 

 the eyes, and two tentacular cirri. 



Eleven bristled segments follow (in one in March only three, and yet the form 

 carried eggs), and they have a dorsal cirrus and a setigerous region ; then about thirty 

 segments bearing the long dorsal swimming-bristles succeed. Each of these has a 

 deeply-cut foot, which increases in size from the first for some distance backward, and 

 has dorsally the cirrus (Plate LXXI, fig. 4), which is of moderate length, and smooth. 



1 It is interesting that Greef, also in December, found a translucent pelagic Saeconereis off the 

 Canaries, and he followed the development of the larvae to the appearance of the first pair of bristled 

 feet (' Zeitsch. f. w. Zool.,' Bd. xxxii, p. 251, Taf. xiv, f. 31—36). 



