20 Papers from the Department of Marine Biology. 
am not able to say whether any stage resembling the Nauplius is passed 
through within the egg membranes, but think it is unlikely. 
I figure here a ‘‘pro-Cypris” stage (text-figure 10) where the typical 
form of the Cypris has been attained, but the secretion of chitin has 
only just commenced and so the appendages have not assumed their 
articulate form. The embryonic antenne are much larger in size than 
their ultimate development would lead one to expect. 
The Cypris larva (text-figure 11) has rather a broad, squat form com- 
pared to that of other Rhizocephala. As Hafele has pointed out, it is 
very much reduced in organisation. The antenne appear to lack 
the “‘appendices sensoriels,’’ which in Sacculina are used for anchoring 
the larve to the hairs of the host. The distal article of the antenna 
is very small and the cement glands which might supply a secretion for 
fixation were not seen in the larve examined, so that it is not clear how 
attachment is effected in the first place. All these points in Hifele’s 
description are borne out by my material. It is supposed by Hifele 
that attachment takes place on a freshly moulted crab, for the occur- 
rence of external sacs on the hairless parts of the carapace must be 
explained in this way, according to the development in place theory; 
but since this theory is no longer tenable, we are left with the onus of 
explaining attachment in some other way. It is possible that cement 
glands are really present, but are seen only with difficulty in preserved 
material. 
THE CHANGES IN THE VISCERAL MASS DURING DEVELOPMENT. 
As development proceeds the larve take up more room, the egg mem- 
branes in which they are contained stretching with their growth. The 
interstitial cells appear to decrease in number and in the later stages 
the interior of the visceral mass consists of a mosaic of developing 
embryos, all in contact with small numbers of interstitial cells in the 
gaps between the egg shells. The mantle, too, as the result of the 
pressure of the embryos, becomes a very thin layer of tissue. 
There is, however, a definite organ in the centre of the visceral mass 
which makes its appearance at this stage and retains its individuality 
until the larve hatch. This is a long thin process, the continuation of 
the peduncular tissue, and it is hardly to be doubted that its function 
is to supply nourishment to the developing eggs. (It is very well 
figured in Hafele, 1. c., Taf. 2, Fig. 14, schw.) Coutiére says, in refer- 
ence to it, that it represents the whole visceral mass; he regards the 
developing eggs as now occupying the ‘“‘mantle cavity” (cavité incu- 
batrice), while the ovarian epithelium has entirely disappeared. As 
stated above, the mantle cavity has no real existence in Thompsonia, 
and in young specimens it is not simply the matter of an ovarian epi- 
thelium, but the ovary occupies almost the whole of the visceral mass. 
