OPHRYOTROCHA PUERILIS. 367 



At Naples Lo Bianco 1 states the ova are deposited from January to May, so that in 

 our country it is somewhat later, but it evidently extends over several months. 



Habits. — It is very hardy in confinement and breeds freely. It crawls actively on 

 the seaweeds and zoophytes or along the glass. 



The description and figures of Claparede and Mecznikow had been overlooked when 

 the first account of the British examples w r as drawn up, but comparatively little alteration 

 is necessary in regard to either. The figure of the maxillse and mandibles given by these 

 authors, indeed, is not characteristic of our forms, and probably considerable variation 

 exists, though the amalgamation of the anterior denticles is different from anything seen 

 in the British forms, which have a row of six separate processes. The lateral view of the 

 foot also (fig. 2f) has been from an injured or imperfectly preserved example. The older 

 authors' views of the body and head, however, are good, and their account and figures of 

 the young are also accurate. They describe and figure an eyeless larva 0*3 mm. long 

 with five ciliated rings, tactile cilia on the prostomium, and a median caudal cirrus. The 

 dental apparatus shows the mandibles and rudimentary maxillae (the joint authors' labrum). 

 Then two lateral caudal cirri are developed by-and-by, and finally feet. When 2 # 5 mm. 

 long two black eyes appear and the ova are ripe. The authors do not allude to the male. 



De St. Joseph (1888) described and figured this species under the name of Paractius 

 •mutabilis, and had found it in considerable numbers at Dinard. He, however, pointed 

 out that it probably fell under the same genus as Staurocephalus minimus, Lang., 8. Siberti 

 Mcintosh, and Ojpliryotrocha puerilis. In the same contribution he figured a young example 

 as Ophryotrocha puerilis, the condition of the dental apparatus apparently having misled 

 him. 



A careful account of this species was given in 1893 by Bonnier from specimens 

 preserved at Wimereux, where it had formerly been found by the distinguished founder 

 of the Laboratory, Prof. Griarcl. Bonnier rightly gives a wide margin for variation in this 

 almost cosmopolitan species, and the dental apparatus especially shows divergences. Thus 

 in the British examples the lateral denticles are much less prominently denticulated than 

 in those from Wimereux. Moreover the terminal lobes of the feet differ slightly. Bonnier 

 shows three or four of the posterior denticles as boldly denticulated, whereas in ours only 

 one (the most posterior) presented this structure. Bonnier criticises the groups of Ehlers, 

 viz., the Labidognatha and Prionognatha, averring that in its young condition (four to 

 fifteen segments) Ophryotrocha is like one of the Prionognatha, whereas in its adult state 

 it resembles a Labidognath. The classification therefore holds only in the adult condition. 

 This author also considers Paractius, Levinsen, from Greenland, as synonymous. It 

 presents the larval character of a band of cilia around each segment. 



Hacker (1896) mentions a larval form with " intertrochalen " ciliated rings. 



Czwiklitzer 2 lately removed the head-segment in one, with the result that degenerative 

 processes followed for six weeks, viz., loss of cirri, bristles, and most of the feet, but a week 

 later there was complete regeneration of the lost parts. If the first segment is removed, 

 the second may take on the character of the head. When the first and second segments 



1 ( Mitth. Zool. Stat. Neap./ xiii, p. 489, and ibid., xix, p. 583. 



3 ' Arch. Entwickelnng./ xix, p. 140, and figs., 1905 ; and < Journ. R. Micr. Soc./ Feb., 1906, p. 28. 



