DEVELOPMENT OF THE ENOPLA. 91 



somewhat less pressure. There are now four eyes, the anterior pair being the larger. 

 Occasionally a few have an additional pigment-speck or two near the posterior eyes. The latter 

 are further apart than the anterior, differing in this respect from those of the young Tetra- 

 stemma, in which the eyes are equidistant in both pairs. The ganglia (A) are large, pale, 

 distinctly outlined, connected by the two commissures, and give off the lateral nerves (n), which 

 approach each other very closely at the posterior end. 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 (6), after which follows an indistinct stylet-region and reservoir. No stylets are 

 visible until much crushed, and then in one specimen two slender spikes, probably from the 

 marginal sacs, were seen. The posterior region of the proboscis bends forward, and becomes 

 lost at c. Shortly after the marginal stylet-pouches in some become very evident, 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 is unarmed (Plate XIII, fig. 12). The specimen had 

 really only granules in its sacs ; but to save multiplication of figures one w T as deleted, and 

 filled in with a correct drawing of stylets from another example. There is no trace of a central 

 stylet, but the basal apparatus has coarse granules, which move with the muscular investment 

 around them, for at this time the latter exhibits distinct contractions. The muscular space (e) 

 behind the floor of the anterior chamber shows indications of an inner and special lining, which 

 forms a transverse boundary in front. The basal structure is less defined than in the adult, but, as 

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

 stylet-sacs a few days afterwards are generally furnished with stylets, but these organs are not so 

 sharp and smoothly finished as in older examples. When the central stylet appears, the granules 

 of the basal apparatus have a more definite shape than represented in the figure. An outline 

 of the two kinds of stylets is given in Plate XII, fig. 5, from the same specimen, and the dispro- 

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

 furnishes its own organs. The central stylet (a) is generally more slender and acute, as well as 

 longer than the marginal (b) 9 the head of the latter being more globular than in the adult. As 

 the specimen increases in age, the disproportion between the stylets lessens — one or more of 

 the marginal 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 contracts with 

 force, so as to propel the granules, and even the glandular lining of the cavity itself, forward to 

 the front of the basal apparatus. The superficial granular glands of the stylet-region are also 

 well developed. 



Some weeks afterwards (and there is no difficulty in preserving them for this period, even 

 without a change of water) four eyes are observed in the majority. The head of the worm is 

 distinctly marked in progression, and the cuticle richly ciliated, a few longer cilia occurring at the 

 snout and tail. The cilia are also very active in the cephalic pits, the openings in which are 

 circular; and there is, moreover, a slight constriction at this point between the two pairs of eyes. 

 The dermal tissues are well seen, and the ganglia still remain relatively large. Every structure 

 pertaining to the proboscis now shows considerable advancement ; and it may be noted that the 

 posterior glandular organ is wider and shorter in proportion than in the adult. In each marginal 

 stylet-sac (Plate XIII, fig. 13) there are at least three well-developed stylets — the heads of which 

 still appear somewhat more globular than in the perfect animal, besides a headless fragment 



