Discovery reports (1934) Discovery reports discoveryreports09inst Year: 1934 272 DISCOVERY REPORTS 1*3 mm. respectively. The head is blunter than the tail and is marked off from the body by lateral opposite furrows and a complete circular chevron groove whose apex points back ventrally. No eyes are visible. The colour is usually bleached but may be yellowish. Anatomy. The epithelium is thick. In one series of sections it was at the head almost twice as thick as the basement membrane, circular and longitudinal muscles together. Farther back on the body its relative thickness was less. I have
Discovery reports (1934) Discovery reports discoveryreports09inst Year: 1934 272 DISCOVERY REPORTS 1*3 mm. respectively. The head is blunter than the tail and is marked off from the body by lateral opposite furrows and a complete circular chevron groove whose apex points back ventrally. No eyes are visible. The colour is usually bleached but may be yellowish. Anatomy. The epithelium is thick. In one series of sections it was at the head almost twice as thick as the basement membrane, circular and longitudinal muscles together. Farther back on the body its relative thickness was less. I have some doubt of the value of comparative measure- ments of the epithelium and muscle layers, for another series shows a thick basement membrane not much stained, and a clear layer of circular muscles, the two together being about equal in thickness to the epi- thelium; it seems probable that bad fixation may be responsible for these differences. The head gland is compact. It opens by a median pore at the tip of the head. There are three strands, one median dorsal and two lying laterally along the rhyn- chocoel. The former nearly reaches the dorsal com- missure. The oesophagus opens into the rhynchodaeum near the snout and enlarges to the stomach just in advance of the brain. The anterior caecum sends forward two diverticula above the lateral nerves which overlap the posterior ends of the dorsal ganglia (Fig. 48), although the relative position of the branches and ganglia is altered by the state of contraction. The single ex- cretory ducts open before the junction of the anterior bocjy caecum with the gut. The proboscis is stout. The armature consists of a main stylet on a pear-shaped base larger than itself and two accessory reservoirs each with one or two stylets. There are ten nerves. The ventral ganglia are a little larger than the dorsal. The cerebral canals appear as furrows on the ventral surface just in advance of the anterior pair of eyespots. They deepen and sink in. The
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