90 DEVELOPMENT OF THE ENOPLA. 



milky substance, whose borders were slowly commingling with the surrounding water, while the 

 numerous coiling jets, like so many miniature wreaths of white smoke from the sides of the 

 worm, were constantly adding to the central mass. This operation lasted only a few minutes, 

 and thereafter the animal moved about the vessel. The female specimen now protruded her 

 snout from the sand and mucus in which she was coiled, and, passing to the side of the 

 cell, deposited in a few minutes a group of ova, about three inches distant from the white 

 edges of the sperm-cloud, retiring again under the mass of sand and mucus. The change 

 of water probably caused the male to eject the matured spermatozoa, and some sympathetic influ- 

 ence, it may be the diffusion of the latter, induced the female at once to evacuate her generative 

 organs, so as to afford the ova the benefit of the male element. A very few ova were found on 

 examination to remain in the body of the female, and they differed in no respect from those 

 deposited in the vessel. The apertures by which the respective elements passed out in these 

 specimens were readily observed as pale specks, each furnished with a central opening, round 

 which for the moment the cilia were well seen. These openings, as in Lineus, occur a little 

 above the lateral nerve-trunk on each side, and even in specimens of A. lactifloreus not fully 

 ripened, pressure forces the contents of the generative sacs in the same direction, although no 

 aperture is visible. 



13. Development. 



The unimpregnated ova in A. lactifloreus (Plate XVI, fig. 8) are pure white, and measure 

 - 7 - 2 -nd of an inch in diameter, the pale spot just before deposition being about s^th of an inch. 

 The ovum has two coats — an external hyaline investment {a), which becomes considerably firmer 

 after extrusion, and an inner membranous sheath (b), of greater delicacy, enveloping the vitellus 

 (c). With the exception of the pale spot the ovum is uniformly granular, the granules on gaining 

 freedom showing active molecular motion in the surrounding water. At a particular point 

 is a very distinct process (micropyle ?) (d), as if from the remains of a tube that led through 

 the outer coat. A few hours after deposition and impregnation the pale spot disappears, the 

 yolk divides into two masses (Plate XVI, fig. 9), and shortly afterwards into four (fig. 10). 

 On the second day almost all the ova are in the mulberry-stage (fig. 11). In seven or 

 eight days the embryo revolves within the capsule by aid of its cilia, and the majority are 

 extruded from the twelfth to the fourteenth day. The young animal is furnished with 

 two eyes before bursting the egg (Plate XVI, fig. 12), and the coarse granular matter and 

 globules of the digestive tract are apparent. In this condition the wall of the ovum is readily 

 ruptured, and no sooner do the young get over their labours of extrusion than they glide rapidly 

 off, head first, in a manner that shows no training is necessary to enable them to progress. 

 They somewhat resemble the ciliated planules of the Hydroid zoophytes and the young of many 

 of the higher annelids. Probably the action of the cilia may have some influence in determining 

 their course. In these young animals, which are just visible to the naked eye as minute specks, 

 the proboscis is marked by a pale space (Plate XVII, fig. 1), that has on each side a dense mass 

 of the granules of the digestive canal. Outside the latter are two pale stripes, broader in front, 

 caused by the nervous ganglia and trunks. Two longer cilia mark the posterior end. A further 

 stage of development (after an interval of about eight days) is shown in Plate XVII, fig. 2, under 



