201 
region“ and he gives good reasons for assuming that this hinder 
part has been regenerated. According to C r oz i er, such cases have 
been referred to regeneration after injury from such bottom feed- 
ing fishes as small sharks. (I have not myself met with any of 
the statements to which Crozier alludes.) 
Reproduction by fission being thus hitherto known to occur, 
under normal conditions, only in the two said species: H. surina- 
mensis (Semper) and Cucumaria planci (Brandt), it is of no small 
interest that the material of Holothurians, collected by Dr. Th. Mor¬ 
tensen on his Pacific-Expedition 1914—16, has afforded the proof 
that this kind of reproduction occurs normally also in Actinopyga 
parvula (Sel.) (syn. H. captiva Ludwig) and Actinopyga difficilis (Sem¬ 
per). The process of division itself could of course not be studied on 
the preserved material, none of the specimens preserved being in 
the act of division. But a careful study of the material in hånd 
has revealed some interesting facts regarding the process of rege¬ 
neration so that it would not seem superfluous to give a short 
record of my observations, accompanied by some figures. 
The specimens of A. parvula (Sel.) were collected by Dr. Th. 
Mortensen on the coral reef at Buccoo Bay, Tobago, B. W. I., 
where this species occurred in great numbers on the underside of 
slabs of old coral at low water mark. 
A. difficilis (Semper) was found under stones and coral blocks 
in a large rock pond near Hilo on the Island of Hawaii. 
A statistic examination of the collection gave the following result: 
A. difficilis: 
40 undivided specimens 
24 regenerating the anal end > 
18 — — oral — 
A. parvula: 
39 undivided specimens ) 
41 regenerating the anal end > 
43 — - oral — 
?o of regenerated 
specimens 
c. 50 % 
c. 65 
In the rich material practically all States of regeneration are 
represented, from specimen just having finished division to such 
where the regenerating part has reached its full size, although still 
distinguishable, on account of its lighter colour, as a newformed 
part of the specimen. 
