DEVELOPMENT OF THE ENOPLA. 93 



through the water like infusorial animalcules ; while, in addition, they are furnished with a single 

 long tuft anteriorly, as observed in Nemertes carcinopkila. The cutaneous textures are not distin- 

 guishable in the slightly compressed animal (Plate XVII, fig. 4) as separate layers, and the entire 

 body has a cellular appearance, probably from the individual elements of the digestive cavity and 

 the cuticular cells and areolae. No eyes are visible. About a week afterwards considerable 

 progress has been made in size (Plate XVII, fig. 5), but the cilia have become shorter in propor- 

 tion to the bulk of the animal ; and though the anterior and posterior ends show a few con- 

 spicuous cilia, the long tuft is absent. The proboscis is situated far back and scarcely recog- 

 nizable. There are now four eyes. In another week the stylet-region of the proboscis is nearly 

 complete, the marginal often appearing before the central stylets (Plate XVII, fig. 6). The usual 

 mode by which the proboscis escapes under pressure is by rupture per anum (Plate XI, fig. 17), 

 an accident to which the structure is peculiarly liable, on account of its posterior position. Thus 

 there is a slight divergence in the development of this species, the young of which move freely as 

 eyeless organisms, provided with a long ciliary tuft ; while in A. lactifloreus two well-marked 

 eyes appear in the young in ovo. The ganglia and lateral nerves, the oesophagus and other 

 tissues are now distinctly outlined. The large size of the proboscis, as compared with the 

 digestive tract, is also conspicuous in this form. In T. vermicula the ova are well advanced in 

 April, and are generally deposited in May. They are surrounded by a loose hyaline capsule 

 (Plate XVI, fig. 14), and the yolk is white. 



Numerous specimens of Nemertes carcinophila were sent from St. Andrews in April, full 

 of ova, and their development could easily be followed out. The newly deposited eggs (Plate 

 XVI, fig. 19) are somewhat ovoid, about -2x0th of an inch in their long and -g^hyth to 3x0th in 

 their short diameter, and appear to possess only a single investment. They are not simply 

 enclosed in a sheath, as M. van Beneden says, but the animal, during deposition, envelopes them 

 and its body in a tough hyaline mucus, afterwards withdrawing itself therefrom, as in Lineus, 

 so that the whole forms a tunnel, with the ova in its walls. The spiral appearance of some of 

 the masses is due to the coiled condition of the animal during deposition. After extrusion the 

 ova pass through the usual stages, and the embryo in each is sometimes ciliated on the tenth day 

 (Plate XVI, fig. 20), although entire dependence cannot be placed on this date, since develop- 

 ment occurs within as well as without the body of the parent. In a short time the young are 

 extruded either with a pair of eye-specks, or without them, and furnished with a very long 

 anterior, and a shorter posterior tuft or whip of cilia (Plate XVII, fig. 7). Moreover, numerous 

 adult specimens are found towards the end of April to contain ova with ciliated young, showing 

 that impregnation, as may easily be understood, can take place through the genital pores. In 

 many ova the embryo has two reddish eyes, and some are extruded from the sacs of the 

 parent in a free state, so that they sail about actively as ciliated pyriform bodies. The motion 

 of the cilia in the oesophageal region in those with eyes is very distinct ; indeed, after the 

 other and apparently more delicate tissues of the animal have become disintegrated, this 

 region is left in full action — dissected out, as it were, by rapid decay. The somewhat globular 

 oesophageal region has probably been mistaken by M. van Beneden for a mouth. The same 

 author fell into the error of supposing that a form having a smooth outline was developed within 

 its progenitor with the long ciliary tuft, the former representing the scolex, and the latter the 

 proglottis ; in short, as he says, a case of digenesis, and not a metamorphosis. But his drawing 

 represents the so-called proglottis furnished with two eyes exactly in the same manner as the 



