358 AMERICAN JOURNAL 



cliial coils very large, the viscera are crushed to the front, and 

 the intestine, which is short and simple, is nearly bent upon 

 itself, though still occupying a median line. In Lingula, 

 where we have a very long and flat sac, the intestine is long, 

 and has ample room for convolutions, but the anus, instead of 

 terminating in a line with the mouth, is thrown to one side, in 

 consequence of this excessive flatness of the sac. The heart 

 will be found on the outer bend of the intestine and actually 

 on the ventral side; the nsrve occupying its homological 

 position. 



"(The manner in which I view the Brachiopoda, if true, 

 will entirely reverse the accepted poles of their structure. 

 What has been considered as dorsal, is here regarded as ven- 

 tral, and what has been considered as anterior, is here re- 

 garded as posterior. Further remarks on this will be made 

 hereafter.) 



" Thus far the balance of sli-ructure has been thrown to the 

 posterior pole of the sac, and though we see a cephalization, 

 or concentration of the muscular system and viscera, toward 

 the anterior pole in Brachiopoda, yet that pole being essen- 

 tially closed, we have no function manifested at that end, ex- 

 cept the degradational one of adhesion. In the Tunicata we 

 have, through continued cephalization, the mouth thrown to 

 the bottom of the sac, or nearer the anterior end, and now the 

 anus terminates behind the mouth, and posteriorly. 



" The heart has also followed the intestine in its rotation, 

 and becomes anterior, and partially dorsal. The nerve mass 

 is still posterior, and occupies a position between the two 

 openings, as in Polyzoa. 



" We have commencing in this group, the Tunicata, that 

 erratic bending of intestine, and varied position in its anal 

 termination, that is witnessed higher up in the scale, and 

 though apparently governed by no law, we can yet trace the 

 progressive movements toward a normal condition, by com- 

 paring Appendicularia, one of the lowest forms of the Tuni- 

 cates, and representing the larval condition of their class. In 

 this form the intestine has a ventral flexure, and terminates 

 on the ventral side. In Pyrosoma it makes an abrupt bend 

 toward the anterior dorsal region, and terminates anteriorly. 

 In Salpa it terminates dorsally, on a line with the mouth, 

 though still anteriorly. In Botryllus it creeps up, and termi- 

 nates nearer the posterior pole of sac, though still dorsally. 

 We have in this genus, and other compound Ascidians, the 

 excurrent orifices of several individuals coalescing, forming a 

 common cloaca for a community. The dorsal fiexture is dis- 

 tinctly seen in Clavellina borealis. In these three classes, 

 namely, Polyzoa, Brachiopoda, and Tunicata, the sac is essen- 



