134 SPIONID^. 



organs " are the source of the generative products, and are, in short, the organs of 

 reproduction. 



Claparede 1 (1863) gives an account of a young Spionid of about eighteen bristled 

 segments, and somewhat resembling Polydora, but differing in various respects, such as 

 in pigment-specks, more numerous branchiae at the same stage, and bifid crenated anal 

 region. It differs from Prionospio in the origin of the branchise, which in that form arise 

 on the thirteenth segment, whereas in Claparede's they begin on the seventh bristled 

 segment. It may be the young of Nerine or Polydora. 



In Malacoceros Girardi, De Quatrefages (1850) described small paired cephalic 

 ganglia, oesophageal connectives, and a double ganglionic chain, the ganglia, however, 

 being slightly marked. A ganglion, moreover, exists at the origin of the visceral nerves 

 from the connectives. The arrangement of the nervous system of Aonis folia cea is similar, 

 though in the figure the anterior ganglia are fused. He (1850) denies that the tentacles 

 of the Spionidae are respiratory, but as they contain ccelomic fluid in their interior they 

 may be indirectly so. He thinks a true branchia has an afferent and an efferent vessel, 

 or a single vessel with lacunae hollowed out in the enveloping tissues. 



The same author, somewhat later (1865), separated this group into two families, one 

 of which, the Neriniens, he regarded as errant, and the other, the Leucodoriens, he 

 placed amongst the sedentary forms. This arrangement has little to support it, and 

 much weight against it; indeed, it serves only to confuse the observer. It is true he 

 speaks of the uncertainties and contradictions in the literature of the subject, but such a 

 method as he adopted was not calculated to promote perspicuity. He arranged the 

 Neriniens according to the structure of the feet, the biramous types being deprived of 

 cirri in Nerine, which had no crotchets, whilst Uncinia had ; whereas Aonia bore inferior 

 cirri only, and Malacoceros and Colobranclms both dorsal and ventral cirri, the former 

 being devoid of eyes, the latter with them. Pygospio had a uniramous foot. The 

 Leucodoriens were placed after the Ariciidae and other sedentary forms. The genera 

 were discriminated by the structure of the feet, which in some are divergent and 

 biramous, and the branchiae superior. In Leucodore the branchiae are inferior; and the 

 third segment is abnormal in Disoma ; but in Polydora it is the fifth or sixth segment 

 which is abnormal. Uniramous feet, again, occur in Spione, while in Spiophanes the 

 feet are uniform throughout. 



In his ' Structure des Annelides sedentaires,' Claparede 2 (1873 — a posthumous volume) 

 gives many interesting features relating to the Spionid^. Thus, in Audouinia filigera, 

 the cuticle, which is thin in sedentary Annelids, and the hypoderm, are pierced by pores 

 and canals for transmitting the secretion of the subjacent follicles. In Nerine cirratuhs 

 the hypoderm is thick on the ventral surface, indeed, he distinguished a superficial 

 fibrillar hypoderm and a deeper stellar connective-tissue layer. The Spionidae have 

 bacilliparous glands. In Audouinia the longitudinal muscles lie between the fibres of the 

 circular coat. The last mentioned is very thin on the branchise and tentacles. In the figure 

 the muscle is outside the hypoderm, a position the author would at once have corrected. 

 The ccelomic epithelium enters the tentacles as well as covers the dissepiments which cease 



1 ' Beobacht. Anat. Entwickel./ p. 72, Taf. viii, figs. 4—6. 



2 ' Annel. Sedent./ pi. xi, fig. 5. 



