LYCASTIS QUADRATICEPS, AN HERMAPHRODITE 

 NEREID WITH GIGANTIC OVA. 



HERBERT P. JOHNSON. 



The possession of unusual characters by any species or group 

 of animals always arouses our interest and invites thorough 

 investigation. Among the Annelida Polychaeta the genus Ly- 

 castis in the family Nereidae has the striking physiological pecu- 

 liarity that a majority of its known species are found living in 

 fresh water as well as in the sea — a thing of rare occurrence in 

 other families of the Polychaeta. 



In addition to the above-mentioned anomaly Lycastis quad- 

 raticeps is an hermaphrodite ; and furthermore, instead of pro- 

 ducing many small ova it develops only a few of relatively colossal 

 size. 



The species was originally described in that comprehensive 

 work of Claudio Gay, " Historia Fisicay Politica de Chile " ('49). 

 The specimens are stated to have been collected at Calbuco, on 

 the Chilean coast, and the brief description and two figures give 

 no information beyond the diagnostic external characters. It was 

 redescribed by de Quatrefages in 1865 (Tome II., p. 500), who, 

 however, added nothing new. 



Nearly a half century later it was rediscovered by Plate at 

 Lapateia, Beagle Canal ; and by Michaelsen, who found it at Punta 

 Arenas, on the Straits of Magellan, living not only in the sea but 

 in brackish water and even in fresh water ; always, however, in 

 places accessible from the sea, so that we may infer that the fresh- 

 water habitat has been recently acquired. These observations by 

 Plate and by Michaelsen have been recorded by Ehlers ('97, '00, 

 and '01), who, however, failed to note the striking sexual idiosyn- 

 crasies of the species. 



When, in 1902, I was engaged in the preparation of an account 

 of certain fresh-water nereids ('03), Professor Michaelson kindly 

 placed at my disposal a few specimens of L. qaadraticeps. With 

 two exceptions they proved to be sexually mature and her- 



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