ON THE DEVELOPMENT OF LINGULA ANATINA. 105 



the straight course tending toward the adult form, and con- 

 sequently no larval organs are produced. In Lingida, likewise, 

 notwithstanding the considerable length of the free-swimming life 

 the development is almost direct. The arm-apparatus may be 

 considered as the onty departure from the rule ; but even this 

 structure persists as such in the adult, only the tentacle and a 

 part of the muscle undergoing retrogressive changes. In Gistella, 

 on the contrary, there is a great deviation from the direct line 

 of development and a true metamorphosis occurs. As true larval 

 characters must be considered the umbrella-shaped head and the 

 posteriorly directed mantle lobes. 



XIII. A LARVA OF DISCINA. 



Lying among the larvae of Lingida I found on one occasion 

 a specimen which attracted my attention by its circular shells. 

 A closer examination made it evident that it was nothing else 

 than a larva of Discina. This has proved to be the only 

 specimen I have been able to secure up to to-day, and my 

 description of it must, I fear, be inadequate, but it seems best 

 to me to record whatever notes I have at hand, if for no better 

 reason than that no living larva of Discina has been observed 

 since 1861, when Fritz Müller secured his material at Desterro. 

 I give a figure of the larva (PI. VI., Fig. 89), as a drawing in 

 natural colors has not as yet been published. 



Although Discina has not yet been collected off Misaki or 

 in the Saga mi Bay, it will surely be discovered there by future 

 explorations, judging from the wandering of this larva into the 

 bay in front of the station. 



In general appearance (PI. VI. , Fig. 89) the present specimen 



