438 MORGAN. [Vol. V. 



no connection with the ectoderm, as affirmed by Bateson, but 

 arise from the peritoneum as a series of sacs attached by a 

 hollow stalk. One may regard Balanoglossus as a modified 

 Trochophore, having a single anterior body segment and a 

 head ganglion under the apical plate. The Trochophora has 

 acquired certain modifications ; viz. dorsal nerve tube, gill slits, 

 etc., which ally it to the Chordata. Bourne records (1889) Tor- 

 naria from the coast of England, believing it to be Tornaria 

 Krdhnii of the Mediterranean. The figure of the larva (13, 

 measuring 1 mm. in length) that he gives, seems to be identical 

 with the New England form figured by Agassiz and myself (Fig. 

 6, PI. I.). The question immediately arises as to whether this 

 larva, if identical, has so wide a distribution, and gives possibly 

 a hint as to the parent form, and locality, of the New England 

 larva. The time of year recorded is also worthy of note, — both 

 are recorded about August 9. (The English form also September 

 21.) The youngest larva figured is at the same stage described 

 by Fewkes (see ante). Bourne did not observe the formation of 

 the anterior (left) enteroccel, and remarks rather carelessly 

 that this body cavity is formed probably from the amoeboid 

 cells found scattered in the segmentation cavity. Unfortu- 

 nately, no evidence at all is given in support of this statement. 

 He says " the ' heart ' (proboscis of Bateson) of Agassiz, Mit- 

 schnikoff, and Spengel makes its appearance ... at this stage 

 as a vesicle lying just above and to one side of the proboscis 

 pore, . . . and an examination of the figures 7 and 8 shows that 

 it is formed as an invagination of the ectoderm just above and 

 to one side of the proboscis pore," as described by Spengel. I 

 have given my reasons for dissenting from this view of Spengel, 

 and I think have discovered earlier stages in the development 

 of the proboscis gland than seen by Bourne. It is interest- 

 ing, however, to note that Bourne believes the anterior right 

 enteroccel to come from mesenchyme, and I believe the pro- 

 boscis gland to have this mode of origin. If these statements 

 were both true, then the identity of the anterior enteroccel and 

 the proboscis gland would be proven, and, moreover, an inter- 

 esting relationship established between the enteroccels and 

 mesenchyme. I cannot, however, accept Bourne's statement 

 of the origin of the anterior left enteroccel without some evi- 

 dence. On the other hand, I believe Goette's statement that 



