NOB. | Balanogtlossus. — 195 
bryology of Echinoderms, and among the larve of the various 
groups of these animals that he collected with his tow net in the 
Mediterranean Sea was this which he named Tornaria from the fact 
that it constantly rotates about its long axis as it progresses through 
the water. He thought it was probably the larva of some Echino- 
derm and finally, after studying as many stages as he was ever able 
to find, decided it to be a Holothurian. Afterward several zoologists 
collected and described the same larva and were deceived as its 
original discoverer had been till finally, in 1869, Metschnikoff,“a 
Russian zoologist, was fortunate enough to see the Tornaria so tar 
transformed into the Balanoglossus as to be able to recognize its 
truenature. The adult Balanoglossus had been well known fora 
long time. But although it was now soon established beyond a 
doubt that Tornaria is the larva of Balanoglossus and not of. an 
Echinoderm its close resemblance to the larva of the latter, particu- 
larly to Auricularia, the larva of the Holothurian, was recognized by 
all who studied it. And I may here add that the advance of knowl- 
edge of both the Echinoderm larva and of Tornaria, even to the 
present moment, has only served to increase the belief in the minds 
of many morphologists that there is an actual genetic relationship 
between the two forms. 
Figures 4, 5, 6 and 7 represent the Tornaria in several stages of 
its development. Figure 7 represents as early a stage as has ever 
_ been seen, the larve having always been captured after they have 
escaped from the egg and betaken themselves to their free swim-' 
ming life. They are very transparent and at this stage very small, 
the specimen here figured being between .2 and .3 of a millimeter 
in length—barely large enough to be visible to the unaided eye, 
excepting it be accustomed to seeking such objects. From its 
extreme transparency the internal organs can be easily seen in the 
living animal. 
On the surface are several thickened bands bearing cilia. In the 
smallest larvee the course @f these bands is comparatively simple, 
as is shown in Fig. 7, c. 6. Were the opposite side of the larva 
to be seen, two more bands would be found in corresponding 
Positions. 
‘14 E, Metschnikoff. Untersuchungen iiber die ‘Metamorphose einiger Seethiere. 
ie Ueber Tornaria. Zeitschr. f. Wiss. Zool., Bd, xx, 1870. 
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