a) MARIE V. LEBOUR. 
Dogiel’s account of the larval stages of A. pygmeus, together with the 
present discovery of the older larvee in medusx, shows a most interesting 
life history. According to him the very young larva hatches out of the 
egg (which contains very little yolk), leaves the protection of the father, 
and crawls on to the Obelia hydroid. In this early stage it has three 
appendages, the first the chelee, the second and third with long thread- 
like ends which are used for attachment to the father directly after 
hatching. It immediately begins to burrow into one of the hydroid 
polyps, and once settled down there undergoes a metamorphosis, the 
second and third appendages atrophy, and three pair of walking legs 
develop. After several moults older larvae appear, which are like the 
adults, except for the incompleteness of the last pair of walking legs, and 
these leave the hydroid and begin to live a free existence. 
The stages found in the medusz correspond to the larval stages after 
the second and third appendages have atrophied. The youngest stage 
seen corresponds with Dogiel’s Stage [IV with the three pair of walking 
legs indicated and the chelz well stretched out in front, which are used 
for clinging firmly to the host. Dogiel has called attention to the fact 
that many larve do not succeed in entering the polyps, and have to 
undergo their development on and not in the hydroid, and now we find 
still another alternative for the larva. <A large proportion of them, 
instead of entering a polyp, must in some way manage to enter a medusa. 
How they do this it is not possible at present to say. Possibly they cling 
to a medusa just as it is escaping from the colony, or perhaps they may 
get into a gonotheca before the liberation of the meduse. One young 
larva in just the same stage as the youngest from a medusa was found 
amongst a colony of Obelia from Laminaria collected below the Laboratory. 
The occurrence of the same larva in various meduse shows that it does 
not strictly keep to one species or genus of hydroid, although Obelia 
seems to be the favourite host. 
The discovery that larval Pyenogonids are carried about by medusze 
must have an important bearing on their means of dispersal, those 
individuals which are in the medusz having much greater chances of life 
than those in the crowded area where the hydroid colony is situated. 
Pyecnogonids swim feebly, and have not much in themselves to help in 
their distribution (see Calman, 1915, p. 6), but in the parasitic habits we 
have an important means of dispersal. Already H. Merton (1906) has 
found a species of nymphon (NV. parasiticum) living parasitically on the 
nudibranch Tethys leporina in the Mediterranean. H. Prell (1909) has 
found nymphon on Lucernaria (in this case eating the tentacles), now we 
find larval forms being carried about in medusz. It is interesting to 
note that a young specimen of Hndezs spinosus (Montagu) was twice found 
