270 Bibliographical Notices. 
is there that the small pelagic animals upon which they feed 
swarm, as also dothe Meduse. Then comes to pass this very 
strange fact, which, however, is none the less proved, namely, 
that the fish, entering into certain natural anfractuosities of 
the Medusa, lodges there, issues thence, returns there at plea- 
sure, and thus becomes its commensal. This is the only way, 
I believe, to explain this kind of association between two 
animals of such different types. It is to be remarked that, in 
‘order to penetrate into the Medusa without lacerating its 
tissues, the fish is compelled to swim on one side, that is to say 
in a perfectly abnormal position. 
I take advantage of this opportunity to make known a new 
case of parasitism. I refer to the discovery of two examples 
of Dorychthys excisus (Kaup), male and female, found living 
in a Holothuria. These two fishes were sent to me from the 
Mauritius in October 1881 by M. de Robillard, with the 
assurance that they were quite alive when he took them out 
of the Holothuria. Unfortunately he could not tell me the 
species to which the Echinoderm belonged. Under any cir- 
cumstances the fact seemed to me the more interesting and 
the more deserving of being noted, as it is, I believe, the only 
case of parasitism hitherto observed in the case of a fish of 
the order Lophobranchii. 
The following are some characters of this Dorychthys which 
may serve to identify the species or to determine the age :— 
Total length 50 millim. Plates 18+15—16. 
BIBLIOGRAPHICAL NOTICES. 
Minute Structure of the Central Nervous System of certain Reptiles 
and Batrachians of America. Tlustrated by permanent photo- 
micrographs by Joun J. Mason, M.D. Series A. Author’s 
Edition. One hundred. Newport, 1879-1882. 
Tur methods of histology have reached a perfection which is 
building up new departments of knowledge ; and among successful 
pioneers in these labours Dr. Mason will always hold an honoured 
place for the technical skill with which he brings the reader face to 
face with the revelations of his microscope, and for the sumptuous- 
ness with which his work is given to the world. No such mono- 
graph has previously come under our notice, for the illustrations of 
a difficult research leave nothing to be desired. Some nineteen 
reptiles and batrachians have been studied ; and the author has 
turned his attention to the structure of the spinal cord, the medulla 
