NEMERTINI 227 



then communicates both with the lumen of the intestine and 

 with the outer world. Therefore the permanent mouth still 

 lies at the place of the blastopore. At about the time of the 

 closure of the blastopore the ciliated embryo breaks through 

 both the embryonal envelope, which is likewise ciliated, and 

 the egg-membrane, to continue its development in the free 

 condition. 



According to Hubkecht, the paired fundaments of two nepbridia (?), 

 which only later would come into connection with the outer world, arise 

 as vesicular structures from the oesophagus, and consequently from the 

 entoderm (for the oesophagus is said to be of entodermal nature). In the 

 development from the pilidium these structures are found on the anterior 

 intestine (Fig. 104 A), which here is of ectodermal nature.^ 



III. — Direct Development. 



A transition from the indirect to the direct development 

 is afforded by the Nemertean studied by Dieck: Cephalothrix 

 galathece. Here a ciliated blastula arises as the result of the 

 tolerably regular cleavage. Dieck is inclined to look upon 

 a wide cup-shaped depression, which makes its appearance on 

 the blastula, as evidence of relationship with the pilidium 

 form, for an extension of the edges of the depression would 

 result in the lateral lobes of the pilidium. But a process 

 which is accomplished later recalls far more the indirect 

 mode of development of other Neraerteans than this outward 

 shape of the embryo does. After the embryo has elongated 

 and has assumed a rather worm-like shape, the layer of ciliated 

 cells covering it begins to be cast off, and under it a neio coat of 

 cilia is imviediately developed. Apparently hei'e also, as in 

 the type of Desor and in the pilidium, the new covering of 

 the worm is formed under the larval skin ; a great simplifi- 

 cation in the mode of development has, however, taken 

 place. Special plates, which enlarge and unite to form the 

 new body-covering, are no longer formed as the result of 

 invaginations of the larval skin, but the body-covering is 



* [These organs have also been recently recognized by Burger (Ap- 

 pendix to Literature on Nemertini) to be nephridia, and their origin is 

 likewise referred by this author to the ectodermal anterior intestine. — K.] 



