STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 
295 
Pedicellina the stage corresponding to fig. 52 of Loxo- 
soma; according to the statements of this observer, the 
“ Entodermsackchen,” originally a solid cell mass, becomes a 
sac enclosing a lumen ; the sac attaches itself to the epiblast, 
and its lumen then opens (secondarily) to the exterior. The 
latter stage undoubtedly exists in Pedicellina, although, as 
explained above, Hatschek's statement that the dorsal organ 
contains hypoblastic elements is probably erroneous. The 
main difference between the brain of Pedicellina (for such I 
consider to be the nature of the dorsal organ in this genus 
also) and that of Loxosoma consists, at the present stage, 
merely in its greater transverse elongation in the latter genus, 
that of the former being represented by an oval sac whose long 
axis is directed transversely. 
Uljanin (5), it may be noted, states that in examining the 
larvae of Pedicellina, he at first erroneously supposed that 
the dorsal organ and the sucker were nervous structures. He 
says (p. 437) : “ Sieht man eigenthiimliche ganglienformige 
Organe, die mit einander durch Commissuren vereinigt sind. 
Dieses Organ sieht einer Ganglienkette so ahnlich, dass ich es 
auch anfangs fur ein solches gedeutet habe. Eine griindlichere 
Untersuchung bewies aber dass eine solche Behauptung 
nicht die richtige war . . . . im Innern dieser Organe 
konnte ich, trotz aller meiner Bemiihungen, nichts Ganglien- 
zellen Aehliches finden.” 
In Loxosoma Leptoclini, before very long after the stage 
represented in fig. 48, there appears on the deep surface of the 
invaginated brain a layer of fibrous tissue (fig. 49 and fig. 52, 
fbr.), which resembles the commissural part of the adult 
ganglion in staining very slightly even after prolonged treat- 
ment with borax carmine, or hsematoxylin. On each side of 
the brain is now found a pigment spot or eye, whose mature 
form is shown in the free larva, fig. 55, o. The eyes make 
their appearance at a time when the brain still possesses a 
conspicuous lumen, which soon after their formation atrophies 
by the mutual apposition to one another of the two cell layers 
forming the walls of the sac ; in the larva which is ready for a 
VOL. XXV. — NEW SER. U 
