72 MORGAN. [Vou. IX. 
Nerve Cord. 
The gill-slits and the nervous systems of Balanoglossus have 
given the most important data for a direct comparison between 
the Enteropneusta and Chordata. The evidence furnished by 
the gill-slits seems to me to be valid, but I think the comparison 
between the nervous systems of the two groups needs a more 
careful analysis than has heretofore been given. Spengel in 
1884 and Morgan in 1891 pointed out that, in the forms 
examined by them, the whole length of the nerve cord was 
formed by a rolling in of ectoderm, while Bateson had described 
in 1884 the central part of the nerve cord of B. Kowalevskii 
as formed by delamination and only the ends by invaginations. 
In the Bahama form there can be no question as to the rolling 
in of the whole length of the cord and the formation of a 
central canal throughout its entire length. 
In 1887 Harmer described the nervous system of Cephalo- 
discus in Vol. XX of the Challenger Reports. ‘The central 
nervous system is developed on the dorsal side of the collar as 
a mass of ganglion cells and nerve fibres lying outside the base- 
ment-membrane of the epidermis. It is, however, continuous 
anteriorly with a similar development of nervous tissue situated 
on the dorsal aspect of the proboscis, and laterally with a well 
developed nerve layer on the dorsal side of the lophophoral 
areas.” In the young bud the nervous system is clearly seen 
to develop from the collar. 
The position of the central nervous-system of Cephalodiscus 
might be compared to the position of the cerebral ganglia of 
Invertebrates in general, and suggests a direct comparison 
between the two. It must be remembered, however, that this 
plate of cells remains in the superficial ectoderm in the adult, 
and no special advantage is gained so far as I can see by such 
a comparison. It is preferable to look upon it as a specializa- 
tion of the ectoderm for nervous functions such as is found in 
Coelenterates and Echinoderms. 
I think no one will doubt the relationship between the 
nervous system of Cephalodiscus and Balanoglossus, the 
former representing the more primitive condition from which 
