104 DORYMENIA ACUTA. 



condition some of these more modified types present a simpler condition than 

 at a later stage. In small specimens of the present species, about 14 mm. in 

 length the various organs, connected with the reproductive system, hold the 

 relations described above but they are far from being functional. The gonad, 

 for example, is clearly paired throughout its entire length and the epithelium shows 

 the merest traces of reproductive activity. The folds of germinal epithelium, 

 that form a most characteristic feature of the adult organ, are commencing to 

 appear on the latero-ventral surface of the gland, and there are slight evidences 

 of a proliferation of cells on the inner wall of each gland. The dorsal aorta or 

 sinus is of unusual size and in some places separates the two halves of the gonad 

 completely, especially in front of the heart, where they are distant from each 

 other by an interval equal to one third the diameter of the body. Thus widely 

 separated they open into the pericardium, which, as in the adult, is of large 

 size (Plate 15, fig. 9). The heart likewise is typical. The ducts leading to the 

 exterior are of essentially the same calibre throughout; the seminal receptacle 

 terminates anteriorly in a relatively long flagellum-like process; the spicule 

 sheaths have developed though there are no traces of the organic basis of the 

 spicules themselves as in decalcified specimens of larger size; and the vesicles 

 opening into the cloaca are both present though their outlets are relatively 

 large. Above all there are no signs of glandular activity. As noted on page 169 

 if these ducts are in part excretory this phase of activity should appear long 

 before sexual maturity and its absence indicates, that these tubes are merely 

 for carrying off sex products. 



In this species the sheath surrounding the nerve bundles is of unusual 

 density or at all events stains with uncommon intensity in haematoxylin, so 

 that branches not over 0.002 mm. have been followed. Owing to this fact more 

 than usual care has been taken to determine the distribution of the more impor- 

 tant trunks. 



The brain, holding the customary position, dorsal to the pharynx, is of 

 medium size and very clearly bilobed. From its anterior half the usual three 

 pairs of nerves arise and at their origin each is connected with two ganglia, one 

 very minute in size. These fibres extend laterally and anteriorly and after 

 branching several times connect with ganglionic masses about the bases of the 

 cirri. 



A pair of very small nerves spring from the middle section of the brain close 

 to the junction of its lateral and ventral surfaces. Each of these proceeds lat- 

 erally and ventrally, and coming in contact with the sides of the pharynx branches 

 and becomes lost among the numerous muscle fibres. 



