140 ALEXANDROMENIA AGASSIZI. 



short and soon divide into a large nunil)er of minor sinuses eommunicatinp; with 

 the gill folds. 



Each gill plate is merely a ciliated fold of the cloacal wall with which it 

 connects anteriorly and laterally. The blood enters the anterior border usually, 

 and coursing through the narrow enclosed spaces finally makes its way laterally 

 to the body wall. Here it vmites with other vessels of similar origin and finally 

 by means of a large canal passes dorsally and enters the heart immediately after 

 uniting with the corresponding sinus from the other half of the body. 



The blood corpuscles are spherical bodies, .0074 mm. in diameter, hyaline 

 in appearance and containing a small, dense nucleus. The leucocytes are remark- 

 ably infrequent, unusually compact, but otherwise devoid of any noteworthy 

 features. 



About the bases of the gills there are great accumulations of gland cells 

 (Plate 36, fig. 19) occupying spaces in the meshwork of muscle strands between 

 the folds and the body wall. They project somewhat into the sinus of each gill 

 plate, and are occasionally penetrated by blood sinuses, but there is no trace 

 of any outlet nor is there any indication of their possible function. Each cell is 

 approximately 0.01 mm. in diameter, and contains a small, spherical nucleus 

 imbedded in slightly vacuolated, granular cytoplasm. 



The nervous system of this species is in an excellent state of preservation, 

 and as the nerves in many parts of the body are more than usually well defined 

 considerable attention has been devoted to this portion of the anatomy. The 

 location of the brain and principal ganglia are the same as in Dorymenia acuta for 

 example, but in the distribution of certain of the nerves differences appear which 

 are here described. The brain (Plate 12, fig. 5) is relatively small, but anteriorly 

 gives rise to the usual number of nerves distributed to the atrial cavity and the 

 neighboring body wall. The united connectives of the lateral, pedal, and labio- 

 buccal systems enter from the side. The first two connectives become differen- 

 tiated a short distance laterally and pursue their usual course through the body. 

 The labio-buccal connective springs from the lateral connective posterior to the 

 union with the pedal and holds its customary position at the sides of the pharynx. 



In Dorymenia there is a large nerve fibre arising from the anterior end of 

 the lateral ganglion and is distributed to the precerebral ganglia about the bases 

 of the cirri; in the present species it is totally lacking. In both species nerves 

 arising from the pedal ganglia are distributed to the walls of the pedal-gland 

 outlet. Numerous connectives unite the lateral and pedal ganglia, and are far 

 from being regular, in several cases uniting with neighboring connectives by 



