338 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



of the sac, curve backwards, and arch over a large cavity (Plate VII. fig. 3, o v) 

 filled with a clear fluid, part of the floor being formed by the anterior fibres of the 

 reservoir. In certain states of contraction the central (reserve) stylet may be 

 seen pressed backwards, so that its butt rests on the latter — a position quite 

 easily attained on account of the yielding nature of the cavity and tissues which 

 lie immediately behind and around it. Some granular streaks, probably due to 

 the granular glands, are also observed passing from the central sac along the 

 arch of the fibres. The granular glands themselves are distinct enough if the 

 specimen is not too much pressed. The peculiar cavity behind the central granu- 

 lar sac might be supposed to assist in the rapid formation of the reserve-stylet, 

 yet it cannot be absolutely necessary for its development, since the stylet is as 

 readily replaced in front of the sac in 0. alba, and others, where no such space 

 exists. Physiologically the cavity may also act as an elastic buffer or cushion 

 when the stylet is driven into any structure, if such ever occurs. The ejaculatory 

 duct is large, and being surrounded by a yielding region, is more mobile than in 

 the typical forms. The clear globules interspersed amongst the looped fibres of 

 the reservoir are numerous, so that under pressure the cavity seems covered with 

 them ; and if pressure is severe, they escape into the reservoir, and pass for- 

 wards into the ejaculatory duct. Posteriorly these looped fibres have a laminated 

 appearance. During examination the walls of the reservoir were frequently con- 

 tracted in the manner shown in the drawing (Plate VII. fig. 3), thus indicating 

 very clearly the presence of circular fibres. The entire region had more trans- 

 lucent walls and greater mobility than in 0. alba, and the coats were somewhat 

 diminished in total bulk posteriorly, so that the channel of communication was 

 short. The glands are large transparent structures, with clear globules in their 

 interior, and in general aspect differ from any hitherto observed. Those of the 

 posterior chamber of the organ were longer than in 0. alba and Tetrastemma. 

 In one specimen several stylets lay in the cul-de-sac of the latter chamber, show- 

 ing that they had passed along the ejaculatory duct, or else had been formed in 

 the cavity. 



The muscular and other structures of the anterior region of the proboscis of 

 0. pulchra present, in transverse section, a slight variation from the common 

 type, as seen in 0. alba. The beaded layer (Plate VII. fig. 1 0, e) is very distinctly 

 marked, and the external angle of the somewhat lozenge-shaped enlargements 

 (longitudinal bands) is connected with the outer layer (g), while a process from 

 the opposite angle passes inwards towards the circular coat (c), so as to cut the 

 great longitudinal layer (d) into a number of separate fascicles, which, in the 

 specimen represented, amount to fourteen. The changes which ensue in the various 

 layers, when the organ is completely everted, are portrayed in the figure ; and 

 the characteristic appearance of the beaded layer (e) is to be noted, as well as the 

 swollen segments of the usually thin external longitudinal layer (/). 



