DORYMENIA ACUTA. 101 



of corpuscles. Anteriorly it passes into the aorta which, passing between 

 the two widely separated ducts from the gonad, becomes a vessel of large 

 diameter. 



The vessels to the gonad, and the exit of these into the visceral cavity and 

 the communication of the dorsal sinus with the numerous channels in the head 

 region are of the usual type. The sinuses of the head are relatively small yet 

 may readily be followed through the anterior pedal gland and about the buccal 

 wall to a small median ventral sinus situated above the outlet of the anterior 

 pedal gland. Above the forward end of the foot this median sinus widens 

 greatly, and during its journey to the posterior end of the body communicates 

 here and there with the visceral sinus and at various points is divided horizon- 

 tally by a muscular septum, thus forming two fairly complete sinuses one above 

 the other. In the region of the coelomoducts the.se channels become sharply 

 defined, though as they approach the cloaca, the ventral one, in frequent commu- 

 nication with the dorsal, gradually diminishes and at the termination of the foot 

 vanishes completely. The remaining ventral sinus has likewise greatly decreased 

 in size in this same region, and communicating frequently with the outlying 

 visceral cavity disappears immediately in front of the cloaca. At the sides of 

 the cloacal cavity and posterior to it the blood probably passes backward in the 

 ventral half of the body, and by means of numerous channels passes into the 

 dorsal half where it is transferred to the heart by several lacunae, the median 

 dorsal one being most clearly defined. The corpuscles are about two thirds the 

 size of tho.se of Proneomenia which otherwise they closely resemble (Plate 35, 

 fig. 13). 



It will be seen (Plate 6, fig. 4 and Plate 9, fig. 2), that the coelomoducts arise 

 from the postero-lateral borders of the pericardium by relatively large openings, 

 and extending forward as far as the anterior extremity of the heart communicate 

 by a narrow canal with the conical seminal receptacle, and by a larger opening 

 with the last section, of larger calibre, which unites with a corresponding tube 

 of the opposite side and by a single median opening communicates with the 

 cloacal cavity. Immediately beyond its inner opening the epithelial lining of 

 each duct is thrown into prominent ridges composed of slender ciliated cells in 

 which there are faint traces of glandular activity, which may possibly become 

 more pronounced during the breeding period. Half way to the seminal receptacle 

 the ridges disappear and the cells become lower, more cubical, and apparently 

 are possessed of cilia. Furthermore throughout this same section of the canal 

 some of the cells of its outer half become much elongated and form strands which 



