132 WILLIAM BATESON. 



specific variations. Most of these points are in accordance with 

 the account given by Spengel for B. minutus and B. clavi- 

 gerus. 



The occurrence of another species of Balanoglossus (B. 

 aurantiacus) on the North American coast has been men- 

 tioned by Professor Leidy (4) in a paper which I have not been 

 able to see ; this species may possibly be identical with the 

 specimens I have examined. On the whole, therefore, I have 

 thought it better to leave the name of the species an open 

 question. 



In this paper I propose to deal only with the history of the 

 early stages in the development of the animal, up to the 

 formation of the layers and the commencement of the nervous 

 system, and to describe very briefly the most important ex- 

 ternal changes which occur in later larval life so far as I have 

 been able to observe them. I hope shortly, however, to give 

 an account of the subsequent development of the organs, and 

 of some points in the anatomy of the adult. 



The animals live at a depth of about eight inches below the 

 surface of the sand, and are generally to be found with their 

 bodies coiled in an even corkscrew-like spiral. The proboscis 

 and anterior part of the branchial region are usually vertical, 

 and the portion of the body posterior to the generative tract, 

 which is about 6 — 9 inches long, is also, as a rule, not spirally 

 disposed, but can be moved up and down a vertical shaft in the 

 sand opening to the surface. By this shaft faecal matters, con- 

 sisting mainly of sand and mucus, are extruded. 



In this manner very characteristic conical coiled casts are 

 thrown up, like that of the earthworm, the section of the coil 

 being, however, elliptical. The whole body is from 8 inches to 

 1 foot in length. 



Fertilisation and Segmentation. — The animals are 

 dioecious. The ovaries lie in an irregular band along the dorso- 

 lateral aspect of the animal, and the testes in the male occupy 

 a similar position. The dehiscence appears to take place by a 

 rupture of the body-wall in both sexes. When the eggs are 

 laid they are small, ovoid, very opaque bodies, of a greyish 



