582 INVEETEBEATA CHAP. 



by Eitter to the endostyle of Ampliioxus ; it is apparently continuous 

 with a lesser ridge of the same kind in the wall of the stomach. 

 The nerve plate is converted into a nerve tube in exactly the same 

 manner as in the New England Toruaria. 



1 DOLICHOGLOSSUS 



We must now devote some consideration to the shortened 

 development of Dolichoglossus as worked out by Batesoii and Davis. 

 Bateson (1884-1885) found that the eggs of the species he worked 

 at (I). JcowalevsJcii), were shed into the soft mud which the parent worm 

 inhabited, and there passed through the whole of their development. 



The eggs were comparatively large (about '4 mm. in diameter), 

 filled with a yellowish yolk and provided with a firm egg-shell. 

 Attempts at artificial fertilization led only to abnormal segmentation 

 and death of the embryo, and so all stages of development had to be 

 procured from the mud, and Batesoii's method of finding them was 

 not a little ingenious. He procured a quantity of mud in which the 

 adults lived, and to this was added a number of adult worms cut into 

 small fragments ; the whole mixture was stirred up with sea- water, 

 avoiding rotatory currents. Then, after waiting a minute or two to 

 allow the agitation to cease, the upper layers of the fluid were 

 siphoned off until the layer containing the fragments of the adult 

 worm was reached. This layer was then siphoned off and carefully 

 preserved. In it were found the fertilized eggs and the embryos and 

 larvae in all stages of their development, since all these were about 

 the same specific gravity as the fragments of the parent worm. 



The embryos in their early stages of development agree precisely 

 with the embryos of Balanoglossus clavigerus as described by Heider. 

 The proboscis coelom is formed as in the Tornaria larva, but the 

 collar and trunk coelomic cavities arise about the same time as 

 hollow evaginations of the gut. When the larva escapes from the 

 egg-membrane, the same stage of development has been attained as 

 is reached by the Tornaria larva just before its metamorphosis. The 

 larva possesses an apical tuft of cilia, and a ciliated band encircling 

 the posterior region of the body, evidently homologous with the 

 telotroch in the Toruaria larva. The whole ectoderm is beset 

 with shurt cilia, but there is 110 trace of the characteristic folded, 

 longitudinal ciliated baud of the Tornaria larva. Two transverse 

 grouves, including between them a narrow transverse ridge, have 

 appeared. This ridge is the rudiment of the collar region. Some 

 distance behind this the first gill-pore appears on either side ; but 

 the collar region grows back till it covers not only this gill-slit, but 

 also the second which is subsequently formed. 



The changes necessary to reach the adult condition are few ; the 

 apical tuft and posterior ciliated band disappear, the prae-oral portion 

 of the larva grows in length and becomes conical, the gill-slits increase 

 in number, and the trunk region grows in length. 



