138 ALKXAXDKOMKXIA ACASSIZI. 



is i)air('d and llic cfiK^ are developed alon-z; the septum while the s])ennat()Z(ia 

 arise more externally wlune tiie wails are often greatly folded. Posteriorly the 

 iialvTS of the gland narrow greatly and assinne the form of comparatively slender 

 canals (Plato 7, fig. 5), which communicate with the pericardium by wide oi^en- 

 ings. Their epithelial lining is apjiarently ciliated and is fashioned into several 

 low longitudinal ridges. 



The coelomoducts arise from the postero-lateral borders of the iierieardium 

 as conijiaratively wide canals, which first extend downward and then forward 

 to join the so-called shell gland at the point where the seminal recei)tacles are 

 located. As usual the shell gland of one side joins the cori'esponding organ of 

 the other and after narrowing to a sleiuler tube opens into the cloaca in the mid 

 line. 



The walls of the coelomoduct (see Plate 20) in the region of the pericardium 

 are comparatively thin, but one third the distance to the seminal receptacle 

 they become thicker, the cells more slender and the ten to lifteen longitudinal 

 folds more pronoimced, a state of affairs which continues to the shell gland. 

 Cilia are certainly present at various jioints antl it is probable that they exist 

 tlu-oughout the duct between the jiericardial cavity antl the seminal receptacle. 

 In the same section small ([uantities of a glandulai' secretion are tleveloped having 

 the form of minute granules which show at first a distinctly acid reaction but 

 after their discharge become more or less confluent and alkaline. Minute 

 (luantities of spermatozoa are also distriliuted throughout this same division 

 of the duct. 



In the single specimen examined the seminal recei)tacle is a small disc- 

 shaped sac attached to the coelomoduct where the iimer and outer portions meet. 

 It is wedged between the bod\- musculature and the shell gland and the slit-like 

 lumen contains a few spermatozoa only. The cells composing the walls are 

 comparatively low and are glandular, the clear seci-etion, small in amount, 

 giving the cytoplasm a vacuolated appearance. 



In this species the shell gland is of enormous size, filling practically all the 

 space between the digestive tract and pericardium dorsally and the body muscu- 

 lature ventrally and laterally. As figured, Plate 20, each half is penetrated by 

 a duct, of about the diameter of the foregoing section, thi'ough which the secre- 

 tion from the surrounding glandular portion makes its way. In the neighbor- 

 hood of the cloaca these ducts emerge from the gland, unite with each other, 

 and forming an S-shaped loop in side view open into the cloaca by a very narrow 

 pore. 



