WITH NOTES ON THE WEST INDIAN SPECIES. 



269 



Vermiform process of Stomochord. 



The stomochord is produced in front into a long vermiform process like that 

 described by Spengel in Schizocardium and Glandiceps. This process consists of a 

 generally solid cord of undifferentiated cells lying in the median septum of the 

 proboscis. It is coextensive with the median septum extending with the latter through 

 about one-third of the length of the proboscis (PI. XXXI. Fig. 36, and PI. XXVII. 

 Fig. 8 a). In front of the median septum the central cavity of the proboscis is an 

 undivided well-defined space. 



The vermiform process is surrounded by a stout basement-membrane but is of 

 unequal calibre. It serves, in great part, for the insertion of the median dorso-ventral 

 muscles of the proboscis ; but often the muscular fibres pass across the centrum of 

 the proboscis apparently without being inserted into the basement-membrane of the 

 vermiform process. 



The economic importance of the vermiform process apjjea7^s to lie in its capacity for 

 producing basement-membrane. 



The dorso-ventral muscles are quite distinct in the median septum itself ; but 

 outside the latter the fibres soon appear to alter their course and are lost in 

 the general longitudinal musculature. On the dorsal side of the median septum the 

 fibres may be observed to pass through the aponeurosis formed by the closely felted 

 connective-tissue fibres which surround the central cavity of the proboscis. This 

 aponeurosis is interrupted at intervals along the ventral edge of the median septum 

 and is never so strongly developed ventrally as dorsally (PI. XXXI. Fig. 3f!). 



On issuing from the median septum, the dorso-ventral muscles form, both dorsally 

 and ventrally, two divergent bundles; and it is these bundles which farther back, 

 bound the lateral surfaces of the dorsal ^ and ventral septa of the proboscis. 



At some points the vermiform process may be reduced to the basement-membrane 

 which surrounds the axial cord of cells, no cell-elements being visible at such places. 



At the bifurcation of the ventral bundles of the dorso-ventral muscles, there is 

 a longitudinal blood-vessel which rises from the basement-membrane of the ventral 

 epidermis about at the level of the anterior end of the vermiform process. This 

 vessel arches upwards from its point of origin until it reaches the position just 

 described when it runs backwards parallel with the vermiform process. It probably 

 connects the ventral dermal vessels of the proboscis with the central blood-space 

 although I was not able to trace its actual connection with the latter. In accordance 

 with Spengel's nomenclature it is to be defined as the ventral recurrent dermal 

 vessel of <S*. porosa. and the characteristic feature is that it occurs entirely in front 

 of and independent of the ventral septum of the proboscis-. The afferent dermal 

 vessel, as in other Enteropneusta [Spengel, Mon., p. 81], occurs dorsally much farther 

 back near the posterior end of the pericardium approximately at the junction of the 

 dorsal truncal vessel with the central blood-space, i.e. in the nuchal region. 



The aponeurosis round the central cavity of the proboscis dwindles out posteriorly 



in front of the glomerular region. 



^ The dorsal septum of the proboscis, as ah'eady mentioned, is formed by the dorso-lateral wall of the 

 pericardium. 



- The dermal vessels of the proboscis are much clearer in the species next to be described, SpengeJia alba. 



