CXVill 
each end of the body are two kidney-shaped air-vesicles, which serve 
partly no doubt for respiration, but partly also as floats. 
From its extreme transparency this beautiful larva offers a very 
favourable object for study, and Dr. Weissmann has described the 
changes which the different organs pass through. His descrip- 
tions also are illustrated by numerous figures. It will be im- 
possible for me to recapitulate his observations, but I will cur- 
sorily refer to a few of those which have struck me as being most 
interesting. 
The large black eye of the full-grown larva, and which is also that 
of the imago, does not exist at birth. The eye of the embryo and 
young larva becomes, as in many Crustacea, only a secondary optical 
organ. 
In opposition to the views of M. Lacaze-Duthiers, Dr. Weissmann 
regards the external sexual organs as appendages, and not as the 
representatives of segments. The internal sexual organs, as appears 
to be the case in all insects, are present even at birth. So also are 
the rudiments of the trachezx, which however do not contain, and indeed 
are not iu a condition to contain air. It is still more surprising that 
some even of the muscles of the imago, as for instance the wing- 
muscles, are distinctly indicated, not indeed by true muscles, but by 
bands of undifferentiated tissue, which gradually enlarge and acquire 
the character of true muscle. 
Dr. Weissmann describes minutely the gradual formation and en- 
largement of the different organs. This is effected by an infolding of 
the hypodermis or cellular layer of the skin, so that the new organ 
does not, as in most other cases, lie inside the old one, but is formed 
by an inverted fold of skin lying inside the body. The new organs 
also arise in the same manner, the thickening and subsequently the 
inversion of the skin taking place beneath one of the sensitive hairs. 
The neurilemma of the nerve proceeding to this hair develops itself, 
according to Dr. Weissmann, into all the soft parts of the new organ, 
whether muscle, trachea or tendon. In the formation of pupal air- 
vesicles, however, a trachea fulfils this function. The external ap- 
pendages of the imago, such as the wings and legs, are formed, though 
not of course fully developed, during the larva stage ; and Dr. Weiss- 
mann refers the position of the antennze to a muscular act on their 
part, for which he brings forward strong reasons, though it is the first 
time, so far as I am aware, that any movement in the external organs 
of the imago has been observed during the pupal condition. From 
