64 CONKLIN — EMBRYOLOGY OF A BRACHTOPOD. [April 4, 



I. (i) There are three sections of the body: (a) the pre- 



oral lobe, (b) the postoral section (collar) which carries 

 tentacles, and (c) the posterior or anal section (trunk); 

 (2) the preoral lobe probably represents the umbrella of 

 the trochophore ; ( 3) the cilia at its margin probably 

 correspond to the preoral ciliated band (Trochus), while 

 (4; the postoral ciliated zone (collar) which carries the 

 tentacles probably corresponds to the postoral band 

 (Cingulum) of the trochophore; (5) this postoral cili- 

 ated zone (Cingulum) runs obliquely around the body, 

 being further posterior on the ventral than on the 

 dorsal side ; (^6) tentacles appear near the ventral mid- 

 line and fresh pairs are added dorsally. 



II. (7) There is an epithelial nervous system, (8) an apical 



plate, ganglion and (in some species) eye spots, and 

 (9) an oesophageal commissure. 



III. (10) The coelom is composed of an anterior unpaired 

 cavity and two pairs of cavities posterior to this (Mas- 

 terman);^ (i 1} the anterior coelom sac arises as an entero- 

 coel, the posterior paired ones as schizocoels ; (12) there 



; is one pair of protonephridia, which end blindly inter- 



nally in connection with excretory cells. 



IV. (13) There is a ventral invagination posterior to the 

 zone of tentacles and a peculiar metamorphosis by the 

 evagination of this invagination; (14) during metamor- 

 phosis the tentacles turn forward, and (15) the anus 

 comes to lie on the dorsal side of the mouth, the intes- 

 tine thus forming a loop. 



Comparing now the larvae of brachiopods with the Actinotrocha 

 we find that, in addition to the general resemblances to the trocho- 

 phore which both show, there are the following special resem- 

 blances between the two : (i) In both brachiopods and Actinotro- 

 cha the postoral ciliated zone (Cingulum) is greatly enlarged and 

 runs obliquely around the body, being farther posterior on the ven- 

 tral than on the dorsal side. (2) In both cases this forms' the 

 mantle or lophophore, though the tentacles or cirri which are borne 

 upon it appear much earlier in Actinotrocha than in the brachiopod 

 larva. (3) Brooks has shown that in Lingula the ventral pair of 



See postscript, p. 70. 



