6 Papers from the Department of Marine Biology. 
The most interesting point in Coutiére’s papers is his daring sup- 
position as to the significance of Thylacoplethus in the origin and evolu- 
tion of the Rhizocephala. He remarks that the adult parasites exist 
on the pleopods in almost the very situation in which the attached 
larvee of Sacculina* are found, and also that the root systems of adja- 
cent parasites, if not entirely independent, are at any rate largely 
localised. These observations show that here at least infection of the 
host takes place by direct metamorphosis of the larva into the adult 
at the position of fixation, without the intervention of such a stage of 
internal parasitism as characterises the life-history of Sacculina. This 
conclusion points to Thylacoplethus as a primitive or even ancestral 
form and explains the “gregarious habit’’ as due to the simultaneous 
fixation of large numbers of larve. 
The latest researches on Thompsonia have been made by Hafele (4) 
and Kriiger (5) on material brought back by Professor Doflein of 
Munich from Japanese waters. The host in the larger number of 
cases was a species of Pilumnus (a Xanthid crab). Hafele was not 
able, owing to the absence of illustrations in Coutiére’s rather meagre 
descriptions, to decide whether his form was identical with T'hylaco- 
plethust or not. But the possession by the latter of a distinct mantle 
and a cloacal opening led Hafele to suppose that the two forms might 
be safely placed in different genera. 
In this paper the first attempt is made to give adequate figures of 
the parasite. Series of sections were cut to trace the course of the 
root system, but unfortunately a curious error of identification of the 
root tissue is made. This is corrected by Kriiger from examination of 
material in the same collection. But both authors agree with Coutiére 
in supposing that each of the external sacs is an individual formed by 
metamorphosis from a Cypris larva. Kriiger alone seems to contem- 
plate the existence of an internal stage in the life-history as a possibility. 
In 1913 Dr. A. G. Mayer, Director of the Department of Marine 
Biology of the Carnegie Institution of Washington, kindly invited me 
to accompany the expedition of his department to Torres Straits. In 
arranging my programme for this purpose, it occurred to me that 
Coutiére’s observations were partly made on specimens from the very 
field of work to which we were journeying. I kept in view, then, the 
interest which an examination of fresh and specially fixed material of 
this form could not fail to possess, and was fortunate enough to procure 
specimens which throw a great deal of light on this obscure form. 
*In reality the larve of Sacculina do not fix more readily on the appendages than elsewhere. 
+‘ La faible extension des racines, leur localisation dans les bourrelets saillant, dus 4 irritation 
causée par les parasites le grand nombre de ceux-ci, leur fixation dans une cupule deprimée de 
dehors en dedans, la presence de parasites adultes tres voisins sur les pleopodes d’ A. malleodigitatus, 
ou de Thompsonia sur les pattes d’un Crabe la ow s’effectuerait surtout l’inoculation des larves 
de Sacculine au stade Kentrogone; tous ces faits montrent que, chez Thylacoplethus au moins, 
l’infestation de l’héte doit se faire par fixation directe des larves 4 leur place définitive, sans |’inocula- 
tion ni le stade de parasite interne qui paraissent caractériser l’évolution de Sacculina carcini 
Thompson.” 
