ON STYLOCHUS PELAGICUS. 31 



iiig peculiar pigment ccllsj similar to those existing in 

 that planarian, it was concluded, before Johannes Miiller's 

 paper was seen, that the larva must belong to Thysanozoon. 

 Johannes Milller compared the rods and pigment bodies 

 of his larva with those of Thysanozoon Diesingii, which oc- 

 curred in abundance in the harbour of Trieste, Avhere, as well 

 as at Marseilles and Nizza, he found the larva. He concludes 

 that the larva cannot belong to Thysanozoon, because, in the 

 most advanced form in which he observed it, in which it has 

 withdrawn its appendages, and taken the common planarian 

 form, it has no tentacles ; further, because the disposition of 

 the eyes is not that found in Thysanozoon. 



I have no doubt that my larva is closely similar to Johannes 

 Miiller^s, probably tbat of a different species of the same 

 genus. The only difference is that I believe that, in the 

 youngest stage, my larva had only six appendages instead of 

 eight, The disposition and number of the eyes agrees per- 

 fectly in both larvoe. I think that the occurrence of the 

 larva in such very distant parts of world, associated in each 

 instance with abundance of an adult Thysanozoon, when 

 taken in conjunction with the presence in it of rod cells and 

 pigment bodies characteristic of that genus, seem to point, 

 without doubt, to its being the larva of the genus in question. 

 It is quite possible that the arrangement of the eyes may 

 become changed as development proceeds. 



The Thysanozoon {yEolidiceros quatrefages) occurring at 

 Zamboangan is a magnificent species, measuring, when ex- 

 panded, as much as 10 cm. in length by 6 cm. in breadth, 

 with the npper surface of a dark purple, and its peculiar 

 villous tubercles tipped with white. Each of the villous 

 processes bears at its tip a pencil of long tactile hairs. 

 Johannes Milller figures, in connection wirh the rod bodies 

 of Thysanozoon Diesingii, fine threads (1. c, Plate XIII, 

 fig. 5^4), and says (1. c, p. 492): " Es gelang an Letztern 

 den Nesselfaden zu sehen der diesen Korperchen die gleiche 

 Bedeutung wie die Nesselorganen der Medusen und Polypen 

 ertheilt." He adds that these threads are scarcely to be seen 

 in the case of the rod bodies of the larvae. I examined most 

 carefully the rod bodies, both of the larva and of the adult 

 Thysanozoon, and especially with a view to seeing threads, 

 but found no trace of them ; and I think Milller must have 

 been mistaken. In a land planarian [Rhynchodemus), oc- 

 curring at the Cape of Good Hope, I found rod cells, in 

 which the elongate rods themselves are coiled up spirally, 

 and from which they are projected as long, thick threads or 

 rods on pressure being ajpplied. I hope to describe these 



