ee? 
NOTES ON THE STRUCTURE OF OIKOPLEURA. 41 
sections, and also as an approximately true-to-nature dia- 
eram of the typical structure of the group. The structure 
of various Appendiculariidee examined whole as transpar- 
ent objects has been described and figured by Huxley, 
Gegenbaur, Fol, Eisen, Sanders, Moss, Chun and others, 
but the method of serial sections has not apparently been 
applied before to this group, and I do not think any 
figures of sections have yet been published. 
The size of the specimen was:—length of the body 1.5 
-mm., and length of the “tail” 4—5 mm. On commencing 
at the rounded posterior end of the body (see Pl. IV. fig. 
9) it is found that the first few sections consist of ovary 
alone surrounded by a delicate membrane, the ectoderm. 
There is no trace of cuticular test on this part of the sur- 
face. Then, after a few sections, a small crescentic or 
lenticular piece of testis begins to appear on each side of 
the ovary and gradually increases in size as it is traced 
forwards. Consequently in some sections near the pos- 
terior end (see Pl. I. fig. 1) the ovary seems to be a single 
median organ placed between a pair of lateral testes. In 
a few sections considerably further forward, however, (Pl. 
Il. fig. 2) we find two lateral pieces of ovarian tissue, 
while the testis 1s a single organ. The fact is both are 
single, but lobed: the ovary being slightly bifurcated at 
its anterior end and having an overhanging dorsal lobe 
near its posterior extremity (see Pl. IV. fig. 9, ov), while 
the testis consists of two great posterior lateral lobes 
connected anteriorly and ventrally (Pl. LI. fig. 8, sp.). 
The outlines of the ova are not distinct, but the germinal 
vesicles and germinal spots are very conspicuous even 
under a low power (PI. I. figs. 1, 2, &c.), while a higher 
magnification shows them as represented in Plate I. fig. 4. 
The spermatic tissue in the testis shows merely a number 
of fine rounded dots in a faintly stained protoplasm, the 
