lOS 



and the mucus colls among them, x 1900, 



Fig. 43. Section of the branchial r;roove Y/hich connects 

 tiie two parts of the gill, x 860. 



Fig. 45. Section of tlie duct of the gland of Deshayes 

 between the two parts of the gill. The epibranchial canal is 

 shown to the left and the afferent branchial vein to the 

 right. The groat variety in the cells in the duct, is ropro- 

 sented. x 1390. 



Fig. 4G. Secition of two tubes of the gland of Deshayes, 

 from a gill la:;;ina. In t?iG walls of the gill lai;iina are 

 shovm sections of the dendritic processes which penetrate 

 among all portions of the glandular structures, x 1390. 



Fig. 47. Coarser and fig. 4S , finer portions of the den- 

 dritic ]■ recesses from the gill lamina of T. navalis represen- 

 ted in fig. 37. The distribution and contents of these 

 structui'es ar'e represented in detail, x 1900. 



Figs. 49-52. Four stages in the development of the struc- 

 tures of the second factor of the gland of Deshayes. x 1900. 



Fig. 53. Ileax't of specimen 2 mm. long, dorsal view. 

 Openings from auricle show througli the walls of the ventri- 

 cle, X 360. 



Fig. 54. Heart of young adult. The antei-ior aorta is 

 represented as turned to one side, and the auriculo-ventric- 



