SOLENOGASTRES. 



353 



the body-cavity is a haemocoele and contains blood; and in the 

 presence of a pericardium which communicates with the exterior 

 by a pair of nephridia. With regard to the latter point, however, 

 it is not quite certain that the structure called pericardiuin is of 

 that nature (it may be merely a conjoined portion of the gener- 

 ative ducts, of which the structures called nephridia constitute 

 the remainder), and it has been maintained that in the Neomeniidae 

 at least the organs called nephridia show no signs of being renal 

 in function. And even if the cavity in question is pericardial it 

 differs entirely from the pericardium of Gastropoda in the fact 

 that it communicates with the gonad, and the generative cells 

 pass through it on their way to the nephridia, 

 through which they are ejected. 



The Solenogastres are marine, but not littoral 

 animals. Hitherto they have been found only at 

 considerable depths from 15 fathoms downwards 

 as far as the abyss, often in association with 

 colonies of Hydrozoa and Actinozoa on which 

 they appear to feed. 



Fam. 1. Neomeniidae. Hermaphrodite Solenogastres 

 with ventral pedal groove, without differentiated liver, with 

 paired nephridial tubes with a common opening. The 

 body is covered with spicules, which are embedded in 

 the cuticle and in relation internally with epithelial 

 papillae. There is a ventral furrow which is free from 

 spicules ; this structure begins in a rather marked ciliated 

 pit, which is placed just behind the mouth and Contains 

 the openings of a large mucous gland, and ends behind 

 by passing into the cloacal depression ; further, it contains 

 along its floor a ciliated projection, which is supposed to 

 be homologous with the Molluscan foot. 



The mouth is anterior and ventral, and leads into a 

 buccal cavity which has muscular walls, and is sometimes 

 protractile ; it is lined by a thick cuticle, and the ducts 

 of the salivary glands and the sheath of the radula open 

 into it. The latter is absent in Neomenia and in certain 

 species of Proneomenia and Dondersia; elsewhere it bears 



several transverse rows of chitinous teeth. The oesophagus is short, the stomach 

 tubular and often provided with an anterior dorsal caecum ; the intestine is 

 straight, and opens into the cloaca, which also receives the openings of the 

 nephridia and of a mucous gland. The liver is represented by several pairs 

 of short lateral diverticula of the stomach. 



The nervous system (Fig. 276) consists of a large cerebral ganglion in front of 

 the buccal mass, giving origin to a stomatogastric commissure with two small 

 ganglia and to two cords on each side the pallial and pedal passing backwards. 

 The pedal cords are swollen into a ganglion below the oesophagus, and into smaller 



2 A 



FIG. 275. Proneomenia 

 sluiteri (after Hu- 

 brecht). mouth ; 

 F ventral furrow. 



