400 TRANSACTIONS OF THE CANADIAN “INSTITUTE. [Vor . VI. 
The filaments, however, have assumed an appearance much more like 
those of the adult, and the histological differentiation of this epithelium 
is quite pronounced. The mesenteries figured are the same as those 
shown in Fig. 10, but of the opposite side of the body. It will be seen 
that in mesentery VI all traces of the glandular streak have vanished, 
but in mesentery V the streak is still persistent, and, indeed, has under- 
gone a progressive development just as those of the perfect mesenteries. 
That this is not because the larva is the young of a macrocnemic species 
is shown by the fact that it is not mesentery VI, the additional perfect 
mesentery in these species, which has retained its filament, but mesen- 
tery V. Probably later stages would show a disappearance of the fila- 
ment of this mesentery also; but the point which is of concern is the 
fact of the development of filaments on these imperfect mesenteries 
whose epithelium is, so far as can be ascertained, at no point in contact 
with ectoderm.* 
I1V.—THE DEVELOPMENT OF THE FILAMENTS IN BUDS. 
The time relations of the ciliated bands and glandular streaks in buds 
is just the reverse of what obtains in the egg embryos, that is to say, the 
ciliated bands are the first to develop, the glandular streaks appearing 
later. . 
In a bud of Z. soctatus 2mm. in length, the stomatodum is already 
formed, and on the edge of the perfect mesenteries, immediately below 
the lower margin of the stomatodeum, the ciliated bands can be seen 
presenting practically the same appearance as in adult polyps. Follow- 
ing a band downwards, it is found to disappear below, and no trace of 
the glandular streak can be found, and no enlargement of the endoderm 
just external to the free edge of the mesentery. Indeed, there is nothing 
to distinguish a perfect mesentery from an imperfect one, below the 
level of the stomatodeum, except its greater width. The free edge of 
both mesenteries is occupied by cells indistinguishable from ordinary 
endoderm, except by their apparently somewhat smaller size. 
The glandular streaks begin to develop, however, soon after this stage, 
since in a bud but little older they were readily recognizable, and the 
ectoderm just external to them had become relatively very high, and 
* Attention may be called to the fact that the discovery of filaments in these mesenteries serves to em- 
phasize the correctness of the conclusions as to the order of the appearance of the mesenteries in the Zoan- 
theze which have been stated by Boveri (1889), and myself (189ra), and I may add that indications of filaments 
on the microdirectives can also be distinguished, though they are much less evident than those of V and VI, 
possibly on account of an earlier degeneration. 
