104 ART. 4. — N. YATSU : 



which have been called the cephalic, thoracic and peduncular. 

 In the larva? of Lingula this division does not occur, but, if we 

 attempt to divide them in this way, we may say the larva is 

 made up of two " segments," the arm-apparatus representing the 

 cephalic " segment " and the remaining part constituting the 

 thoracic. The peduncle of the Ecardines cannot be homologized 

 with that of the Testicardines from the morphological nor from 

 the embryological point of view. 



The upward reflexion of the mantle which at first covers the 

 peduncular region in the larvœ of Cistella is not seen at all in 

 the course of development in Lingula. In the latter the mantle 

 grows anteriorly ab origine as in Terebratulina (Morse). 



In Lingula the cirriare formed at an early stage and later 

 on become the active organs of locomotion, while in Cistella the 

 head region takes the form of an umbrella and serves tem- 

 porarily (i.e. for a few hours) as a swimming organ. In Disci?iisca 

 and Lingula, on the other hand, there is an evident adaptation 

 to a long free-swimming life. The cirri appear in Lingula as 

 hillocks in a position which corresponds to the cephalic region, 

 while in Cistella they are formed at the submarginal part of the 

 mantle, the tentacle being absent in that genus. We may, 

 therefore, distinguish in the formation of cirri two methods : in 

 one they are formed on the mantle (Cistella), and in the other 

 on the cephalic region (Terebratulina, Lingula). As far as this 

 point and some external changes are concerned there is a strik- 

 ing resemblance between Lingula and Terebratulina. Comparing, 

 moreover, Morse's figures 46-77, 90-91 ('73 a) with my own 

 (PI. HI.) we can at once perceive a striking similarity in the 

 formation of the mantle, shell, etc. 



In Terebratulina development does not deviate at all from 



