ON THE DEVELOPMENT OF EINGULA ANATINA. 57 



preparations (PL VI., Fig. 82, * ). This structure cannot be 

 an artefact ; it perhaps forms a part of the ileo-parietal band. 



h. Mesenteries. 



In the free-swimming larva? all the mesenteries found in the 

 adult are present, viz. : two mesenteries sensu stricto (dorsal and 

 ventral), the gastro-parietal band, the ileo-parietal band and the 

 intestinal mesentery. The last two are especially difficult to make 

 out in well fed larvse, for in such cases the liver and muscles 

 occupy the whole body cavity. In poorly fed larvae, on the 

 contrary, the alimentary canal is greatly reduced in size, and 

 hence the mesenteries are fully extended. Such specimens should, 

 of course, be selected for study. 



The ventral mesentery (PI. V., Fig. 77, PL YL, Fig. 82, 

 and PL VIL, Figs. 99, 105, vt. mes.) is a median septum, which 

 extends between the posterior part of the oesophagus and the 

 anterior part of the ventral body wall. While it is connected 

 anteriorly with the posterior concave face of the ventral ganglion 

 (vt. gn.), its posterior border is unattached. This mesentery 

 consists of two layers closely applied to each other. In a sagittal 

 section we can determine the spindle shaped nuclei of the com- 

 ponent cells. 



The dorsal mesentery (PL VI., Fig. 87, and PL VIII., 

 Figs. 122, 125, 126, dr. mes.) is a very narrow septum, which 

 can be seen in a sagittal section. In examining transverse sections 

 we find that it bisects the anterior out-bulging of the body 

 cavity (Erker of Blochmann), connecting the oesophagus with 

 the dorsal body wall for a distance of 80-90 /a Posteriorly it 

 reaches the point of bifurcation of the anterior dorsal lobe of the 



