92 DEVELOPMENT OF THE ENOPLA. 



or two, and a few clear granules. The normal position of these organs in the marginal 

 pouches seems to be transverse. The stylet on the central apparatus is completely formed, and 

 likewise has a somewhat globular head. The muscular cavity (e) is kept in constant jerking 

 contractions under pressure, while the posterior part (0) is quite still. The other structures, such 

 as the cells of the digestive cavity, have made corresponding advancement, but no blood-vessels 

 are apparent. It may be mentioned, in passing, that the cuticular tissues of these domesticated 

 examples become less transparent than in the wild forms brought from the rocks, and the 

 examination of the internal organs is consequently interfered with. In these young animals also 

 (under pressure) the proboscis generally escapes by rupture at the posterior end, as in Tetra- 

 stemma dorsalis, probably by passing through the anus. In the adult protrusion rarely occurs 

 posteriorly, but almost invariably anteriorly. 



The ova of N. gracilis (Plate XVI, fig. 15) are much smaller than those of A. lactijloreus, 

 and when first deposited slightly adhere together, so that they may be pushed en masse, but they 

 afterwards lie flatly on the bottom of the vessel. Each likewise possesses two coats. The vitellus 

 is dull yellow. Though there is no doubt the spermatozoa in this, as in other species, 

 rapidly diffuse themselves throughout a large quantity of water, yet they were applied directly to 

 the ova by means of a pipette. In about four hours many were adhering to the exterior of the 

 hyaline coat, others were within it, while a few seemed to have penetrated both capsules 

 (Plate XVI, fig. 16). At the sixth hour cleavage has proceeded much further, so that many 

 present the usual mulberry-aspect. In A. pulcher the ova in situ have a beautiful rose-red 

 colour, with a clear spot in the centre. Each ovisac in the middle of the body contains from 

 twelve to twenty ova, therefore it is unlikely that this is a viviparous species, unless a single 

 ovum only happens to be detained in an ovisac here and there, impregnated and developed. 

 Numerous specimens of this form have been perseveringly forwarded from the deep water 

 of St. Andrews Bay for several seasons, since I was anxious to watch the development ; 

 but, unfortunately, the great delicacy of the females at the time of * deposition has hitherto 

 frustrated my efforts. Towards the end of June and beginning of July (at which period the ova 

 are matured) the females frequently break themselves in pieces, or discharge their ova in a mass 

 only to perish in their midst. The males, although their spermatozoa are fully developed, do not 

 appear to fecundate the female products. After deposition the ova have a delicate yellowish-red 

 hue, with a pale, translucent spot, and a somewhat bulky hyaline investment. Like the coloured 

 ova of many animals, they are blanched by death. The ova (Plate XVI, fig. 17) are matured in 

 Nemertes Neesii from the end of March till June, and some even are loaded with ova in 

 November. On deposition they are simply spread out on the bottom of the vessel, and uncon- 

 nected by mucus. The yellowish yolk is surrounded by a fine translucent coat more than twice 

 its diameter. The same delicacy in the ripe females and the non-fecundation of the ova by 

 the males have prevented the study of their development. In Ampkiporus spectabilis the 

 ova, which were deposited by a captive specimen in November, had a white yolk and a loose 

 transparent investment, but as they had perished before they were noticed the colour is 

 uncertain. 



The young of Tetrastemma dorsalis are found in swarms beside the adults in the beginning 

 of July and September. They are so mobile that the body scarce retains the same shape for 

 two consecutive seconds, though approaching a cylindrical form in general, especially when swim- 

 ming (Plate XVII, fig. 3). The surface is coated with long cilia, by aid of which they are piloted 



