On the Rhizocephalan Genus LPR, etc. 21 
It is interesting, however, to compare this organ with the so-called 
‘“‘spadix”’ in the sporosacs of the Hydromedusze. Here we have an 
exceedingly degenerate form of the medusa, with the germ cells lying 
between a single layer of ectodermal cells and the endodermal core. 
This latter is the ‘‘spadix’”’ and it forms a tube which may be greatly 
elongated and even branched, wandering in the midst of the generative 
cells. In the general simplification of structure it is thus elaborated, 
no doubt, to supply nourishment to the developing eggs. But the 
organ described in Thompsonia is by no means so definite as this. 
THE LIBERATION OF THE CYPRIS LARVZ. 
In Coutiére’s first note upon Thylacoplethus it is clearly stated that 
a cloacal aperture is present, which is, however, closed by ‘‘le paroi 
externe du manteau,”’ by which I understand that the protoplasmic 
part of the mantle is penetrated by an aperture, but the chitinous 
envelope is entirely continuous. He believes that the embryos are 
liberated by a moult. Hafele, however, denies the existence of a 
cloacal aperture in the mantle of those species of Thompsonia which 
came under his notice. In 7. japonica he states that the larve are 
finally freed by a longitudinal splitting of the chitinous envelope (I. c., 
Taf. 1, Fig. 1). But in a second unnamed species every external sac 
possesses a genital pore—that is, an opening in the chitinous envelope 
closed by a lid which falls away at the appropriate time. The agency 
of a moult is not required. 
An investigation of my own material leads to conclusions in harmony 
with those of Coutiére. In one example a number of the external sacs 
were more or less empty. All these had lost their chitinous envelope, 
save for a frayed collar round the peduncle. A small aperture was 
situated at the apex of the sac in the mantle and this gave a definite 
outlet for the embryos. This is represented in text-figure 5. The 
aperture must, however, make its appearance at a late phase of devel- 
opment; for, although it is such a regular and definite feature here, no 
signs of such an organ occur in any other specimens in my possession. 
It seems likely that the description which Hafele gives of the larve 
of T. japonica escaping by means of an irregular rent in the chitin is 
an observation of an accidental case. With regard to the definite lid 
observed in another species, this may constitute a true specific dis- 
tinction. 
THE FORMATION OF NEW EXTERNAL SACS. 
When the Cypris larve have all escaped nothing is left but a hollow 
sac (cf. text-figure 5). As the visceral mass thus disintegrates with the 
progress of the development of the larvz, the question naturally arises 
whether the existence of the parasite is terminated at the birth of 
