STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 279 
being indicated on the exterior by constrictions, whilst in 
glycerine preparations made with osmic acid and picrocarmine 
it has been possible to observe the nuclei of the perforated 
cells, seen also with less certainty in the living condition. 
My observations on the nephridia of Loxosoma are confined 
entirely to the adult, but from the analogy of Pedicellina 
there can be little doubt that the larva also is provided with an 
excretory organ. 
Although the nephridium described above differs in a very 
marked degree from that of the Brachiopoda, it has the 
closest possible similarity to the head-kidney of many Trocho- 
spheres (see Hatschek’s papers on Polygordius (17) and 
Echiurus (25). The resemblance between the nephridium of 
Loxosoma and the head-kidney of the larval Polygordiu 
is, however, more striking than could have been anticipated, 
since Fraipont (43) has shown that each branch of the head- 
kidney of the larval Polygordius ends blindly, and has not 
in reality the form of a ciliated funnel opening into the body 
cavity. The probability that the excretory organ of the adult 
Loxosoma is to be regarded definitely as a head-kidney is, 
however, most clearly shown by an inspection of the results of 
the researches of Eduard Meyer on the head-kidneys of various 
Annelid larv@e. Dr. Meyer was kind enough, during my stay 
at Naples, to show me his drawings (at present unpublished) 
of these structures, which resemble the nephridia of Loxo- 
soma in a more striking manner than does even that of 
Polygordius, the similarity being obvious in the number of 
the excretory cells, in the relative size of the lumen in different 
parts of the organ, in the mode of termination in a flame-cell, 
and in other points. 
The Trochospheral head-kidney opens to the exterior on 
each side in front of the anterior end of the ventral nerve-cord, 
as is the case in the Echiurus larva (Hatschek), in the adult 
Loxosoma, and (Joliet) in the adult Pedicellina. Al- 
though it is by no means impossible that fine apertures may 
really exist in the proximal end of the head-kidney of Loxo- 
soma, it is probable that the flame-cell termination, situated 
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