1902.] CONKLIN — EMBRYOLOGY OF A BRACHIOPOD. 63 



repr^ented in the brachiopod larva by the circle of longer cilia 

 found at the base of the preoral lobe (see Kowalevsky's figures of 

 Argtope \bx\^); the postoral ciliated band (7) is probably repre- 

 sented by the mantle, which attains a much greater development in 

 the brachiopod larva than in the ordinary trochophore ; the adoral 

 ciliated furrow (8) is represented by the anterior mantle furrow ; 

 the fact that adult brachiopods have an epithelial nervous system 

 (11) has long been known, and I have observed the beginnings of 

 such a nervous system in the larva of Terebratulina ; I have also 

 observed (p. 55) the apical plate and ganglion (12) and the ventral 

 plate and ganglion (13) in Terebratulina ; only the beginnings of 

 the oesophageal invagination are shown in the oldest larva which I 

 have studied, but it is evident from its position that after it joins 

 the stomach the alimentary canal will be horseshoe-shaped (15) ; 

 the stomach in Terebraiulina larvae is retort-shaped (16) and the 

 intestine reaches to the posterior end of the larva (17). 



In addition to these more important characteristics the larvae of 

 Cistella, Thecidium or Terebraiulina agree with the trochophore in. 

 the possession of the following characteristics : Bilateral symmetry 

 (i), blastopore and anlage of mouth on ventral side (2), ventral 

 blastopore groove (9) and general ciliation of body (10), mesoderm 

 partly mesenchymatous, partly epithelial (18) ; finally ventral and 

 dorsal longitudinal muscles (20) are present in the peduncle of 

 Cistella. These brachiopod larvae also agree with many chaetopod 

 larvae in the possession of ectodermal seta sacs and provisional 

 setse. 



The points in which the larvae of testicardinate brachiopods 

 differ most from the trochophore are in the absence of mouth and 

 anus and the lack of a protonephridium. In the Ecardines how- 

 ever both mouth and anus are present during larval life, and in all 

 brachiopods a single pair of nephridia appears after the larval 

 period. The absence of these larval structures therefore indicates 

 a retardation or less perfect development of the larval brachiopod 

 as compared with the typical trochophore. I believe therefore 

 that the brachiopod larva belongs unquestionably to the trocho- 

 phore type. 



(b) Cofnparison with Actinotrocha. 



The larva of Fhoroms, while showing many peculiarities, bears 

 a most decided resemblance to the trochophore. Among its prin- 

 cipal characteristics may be enumerated the following : 



