180 Dr. T. Williams on the Mechanism of Aquatic 



are contiguous, and the anterior eyes of the four intermediate 

 ones forming the trapezoid, which are near to each other, are 

 the smallest and darkest of the eight. The legs are provided 

 with hairs, and have a yellowish brown hue ; the anterior and 

 posterior pairs, which are the longest, are equal in length, and 

 the third pair is the shortest ; each tarsus is terminated by three 

 claws ; the two superior ones are curved and slightly pectinated, 

 and the inferior one is inflected near its base. The palpi 

 resemble the legs in colour. The abdomen is oviform, hairy, 

 glossy, convex above, and projects over the base of the cephalo- 

 thorax; it is of ^ pale brown colour, with obscure spots of a 

 deeper shade, the under part being rather the darkest; the 

 sexual organs have a reddish brown hue, and their anterior 

 margin is prominent and semicircular. 



The colours of the sexes are similar. The male has the 

 humeral joint of its palpi curved towards the cephalo-thorax, 

 which has a narrow^ indentation immediately behind each lateral 

 pair of eyes; the radial is larger than the cubital joint and pro- 

 jects a strong obtuse apophysis from its extremity, in front, 

 towards the inner side ; the digital joint is somewhat oval, with 

 a large lobe on the outer side ; it is convex and hairy externally, 

 concave within, comprising the palpal organs, which are highly 

 developed, complicated in structure, with a curved prominent 

 process at their base, on the outer side, another, situated under- 

 neath, which has its extremity enlarged and depressed, and two 

 long, contiguous, filiform, black spines, originating near their 

 base, on the outer side, which pass obliquely downwards, and 

 curving round their extremity, extend considerably beyond the 

 termination of the digital joint : the colour of these organs -is 

 red-brown. 



Early in October 1853 both sexes of Neriene herhigrada, in S 

 mature state, were detected among coarse herbage and moss 

 growing in woods on the northern slope of Gallt y Rhyg. Like 

 Neriene sulcata, this species makes a near approximation to the 

 spiders of the genus Walckenaera. 



XVllI. — On the Mechanism of Aquatic Respiration and on the 

 Structure of the Organs of Breathing in Invertebrate Animals^ 

 By Thomas Williams, M.D. Lond., Licentiate of the Royal 

 College of Physicians, formerly Demonstrator on Structural 

 Anatomy at Guy^s Hospital, and now of Swansea. 



[With two Plate.] 



{Continued from p. 137.] 



The orbit of the blood-proper in the Annelid is conducted in 

 obedience to the simplest hydraulic principles. The Annelid is 



