GEROULD: CAUDINA. 
35 
however, Hamann (’84) has found that, although the arrangement 
of muscle layers in the pharynx and stomach is the same as in 
Caudina and Cucumaria, in the small and large intestines the longi¬ 
tudinal muscle layer lies outside the layer of circular fibers. 
The muscle fibers of the pharynx in Caudina (Plate 2 , figs. 13 and 
14), like those of Synapta as described by Hamann, differ from those 
of the longitudinal and transverse muscles of the body-wall in that 
thev are more slender. In Caudina the formative cell and the 
t/ 
nucleus, which is oval and about 7 /x in length, are situated upon one 
side of the axis of the fiber (Fig. 14). The earlier statement of 
Hamann (’83), that in Synapta the nucleus is embedded within the 
contractile substance, has since been acknowledged by him (’84, p. 
95) to be incorrect. 
In Caudina the structure of these muscle fibers affords no indica¬ 
tion that they have developed from mesenchyme cells. Ludwig 
(’91i>), moreover, expresses the opinion that these fibers in Cucu¬ 
maria Planci, the ontogeny of which he has investigated, are certainly 
not mesenchymatous in origin, but are derived from cells of the 
enterocoel which lie closely against the wall of the primitive pharynx 
( Vorderdarm). On the other hand, Selenka (’83) states that the 
circular muscle fibers arise from mesenchyme cells, and Semon (’88) 
likewise finds that in Synapta both the circular fibers and the 
underlying longitudinal fibers are mesenchymatous. The mesen¬ 
chyme cells apply themselves to the wall of the primitive pharynx 
in the Auricularia stage, and send out two or more processes in the 
direction of the future muscle fibers; the processes of the different 
cells unite; and thus, while each fiber is the product of several cells,, 
a single cell takes part in the formation of several fibers. 
Further investigations into both the structural conditions and 
the development of the muscle fibers in holothurians are necessary 
in order to prove whether they arise in part from mesenchyme. 
Hamann’s description of the circular pharyngeal fibers in Synapta 
does not furnish any evidence whatever to corroborate the state¬ 
ments of Semon just given as to their origin and structure in the 
larva. Metschnikoff (’84) denies that they arise from mesenchyme 
in Synapta, and Ludwig, as already stated, is decidedly of the ■ 
opinion that in Cucumaria they arise from cells of the peritoneal 
epithelium. Finally, my studies of the circular fibers both of the 
pharynx and reproductive tubules of the adult Caudina afford me 
