BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 367 



days) is shown in Plate IX. fig. 2, under somewhat less pressure. It will now 

 be observed that there are four eyes, the anterior pair of which are largest, and 

 correspond to the first pair. Occasionally a few have an additional pigment- 

 speck or two on one side of the posterior pair. The anterior pair are nearer each 

 other than the posterior, differing in this respect from those of the young Tetras- 

 temma, whose eyes are equidistant in both pairs* The two ganglia (A) are large, 

 pale, distinctly outlined, connected by the two commissures, and give off the 

 lateral nerves (w), which approach each other very closely at their posterior 

 termination. The oesophageal sac (j) behind the ganglia is well defined ; and 

 two pale streaks mark the cephalic sacs (m). The proboscis has its anterior 

 opening, and the first region (a) its glands, the posterior border being marked by 

 a transverse line (b), after which follows an indistinct stylet and reservoir-region. 

 No stylets are visible until much crushed, and then in one specimen two slender 

 spikes, probably from the lateral sacs, were seen. The posterior region of the 

 proboscis bends forwards, and becomes lost at c. Shortly after this the lateral 

 stylet-pouches become very evident in some, opening by a short and wide tube 

 into the floor of the anterior chamber, and either containing granules or small 

 stylets, while the central apparatus has no stylet (Plate VII. fig. 6). The speci- 

 men had really only granules in its sacs ; but to save multiplication of figures 

 one of them was deleted, and filled in with correct drawings of stylets from 

 another example. There is no trace of a central stylet, but the central sac is 

 filled with coarse granules, and they moved with the muscular setting around 

 them, for at this time the latter showed distinct contractions. The muscular 

 space (e) behind the floor of the anterior chamber shows traces of an inner and 

 special lining, which forms a transverse boundary in front. The basal sac is irre- 

 gular in outline at present, and the shape less defined than in the adult, but, as 

 development advances, the form of the " awl-handle" becomes more characteristic. 

 The lateral stylet-sacs in a few days afterwards were generally furnished with 

 stylets, but these organs were not so sharp and smoothly finished as in the older 

 examples. When the central stylet appears, the granules of the basal sac have a 

 more definite shape than represented in the figure. An outline of the two kinds 

 of stylets is shown in fig. 6, Plate VIII., from the same specimen, and the dispro- 

 portion between them is evident, thus confirming the previous statement, that 

 each apparatus furnishes its own stylets. The central stylet (a) is generally more 

 slender and acute, as well as longer than the lateral (p), which have a more 

 globular head than in the adult. As the specimen increases in age, the dispro- 

 portion between the two sets of stylets lessens — one or more of the lateral being 

 equal to the central in size. The long posterior chamber of the proboscis now 

 contains the peculiar fluid with moving granules, and the reservoir sometimes con- 



* It is curious that in the young of Planaria also four eyes should be a common arrangement : 

 indeed, they are present in some species before the embryo leaves the egg. 



