Reproductive Organs, &c. o/'Arenicola. 299 



and elasticity of the tube, whilst those that were free were 

 readily cut. 



The animals were examined in the living state, and some 

 interesting points noted. In none of them was there any 

 sign of gills ; otherwise they agreed with the description 

 given by Benham. There were two kinds of ventral chaitae 

 (PI. XV. fig. 9), however — one with a single prong like that 

 of the adult, but more curved, the other with two. 



The vascular system was easily traced through the trans- 

 parent body- wall, and was of a distinct red colour. The 

 heart expanded and contracted regularly, the time between two 

 complete expansions being 4"3 seconds. The digestive glands 

 lying close beside the heart were doing the same, but not so 

 regularly, and taking a much longer time — 11 to 16 seconds. 

 Of the blood-vessels the most distinct was the ventral, whilst 

 there were two little red swellings ventrally — one near the 

 mouth, the other about the fourth somite. 



The nephridia appeared as simple elongated tubes. 

 In the head-region (PI. XIV. tigs. 11-1-3) there is very 

 little sign of the pit on the dorsal surface of the prostomium 

 which is present in the adult. In section a slight depression is 

 noticed behind the position of the brain on the dorsal surface, 

 and this may be a sign of the beginning of the formation of 

 the pit. 



The pharynx is muscular and the body-cavity round it is 

 filled up by loose mesenchyme-cells, which are not compact 

 enough to form a definite tissue, but nevertheless seem to be 

 contractile. The pharynx seems to be eversible, as in the 

 adult, because in the specimen from which the sectional 

 drawing (PI. XIV. fig. 12) was made the pharynx was folded 

 back towards the mouth. The epidermal cells of the prosto- 

 mium are elongated, cylindrical in form, with yellowish 

 contents of a granular nature. All the epidermal cells covering 

 the first two somites contain this granular matter. 



Within the prostomium the mesenchyme-cells surround 

 ventrally a large space, dorsally the supraoesophageal ganglion 

 or brain. Tiiis brain, which has the appearance of " punct- 

 substance," occupies a large portion of the interior of the 

 prostomium. Dorsally it seems to be covered only by the 

 mesenchyme-cells, and it looks as if the whole of this part 

 were turned in to form the pit of the adult. Anteriorly nerve- 

 filaments pass from the brain to end in the epidermal cells of 

 the prostomium. Posteriorly in the median dorsal line 

 scattered nerve-filaments pass backward, whilst at the sides 

 filaments stretch to the otocysts and the commissures con- 

 necting the brain with the suboesophageal ganglia. Ventrally 



