398 Miscellaneous. 



menon, the occurrence of which they were led to suppose by observing 

 the difference between young and adult larvae of Gastrus. 



The investigation of the cause of this change increases the interest 

 attaching to the observations. In a larva living in the same way 

 from its exclusion from the egg to its change to the pupa state, such 

 a cause can hardly be discovered ; but it is otherwise with the larvae 

 of the (Estridce, which must wander to the place where they can 

 attain maturity. In this respect the CEstridcB are divisible into two 

 groups, the egg-laying and larviparous forms. To the former belong 

 Gastrus and Hypoderma ; to the latter, Cephalomyia and Cephe- 

 nomyia. In the former genera, the larva has to get into the 

 stomach or under the skin, as the eggs are deposited by the imago 

 upon hairs. In Cephalomyia and Cephenomyia the female injects the 

 maggots into the nose of the animal on which they are parasitic. 

 The greatest difference between the young and adult larvae occurs in 

 those which have the greatest migration to perform, — consequently 

 in the larvae of Gastrus and Hypoderma. 



The author's observations were made on numerous larvae of Hy- 

 poderma Diana, n. sp., from the skin of the Roe. 



First stage (duration unknown, but probably very long, as the fly 

 appears only for a few days in May, and the larvae are found in this 

 stage in the following February. The end of January and beginning 

 of February may be regarded as the period of transition to the second 

 stage). — In this stage the larva grows to a length of 6| lines, but 

 remains nearly cylindrical and scarcely 1 line in diameter. Anterior 

 extremity rounded off ; posterior extremity like the anterior, or the 

 last three segments attenuated into a tail, at the pleasure of the larva. 

 Buccal organs very smalL Buccal orifice funnel-shaped ; above it 

 projects a straight spike, which rests upon a transverse chitinous 

 piece concealed in the oesophagus, from which on each side a chiti- 

 nous arch proceeds backwards and terminates in a shovel-like plate, 

 as in almost all larvae of flies. The shovel-like plates are on each 

 side of the oesophagus, and their faces are vertical. 



Close to the first-mentioned spike are two hooks (one on each 

 side) ; these are bent at right angles, and their free ends are directed 

 outwards and downwards. They can be moved so as to form a single 

 point with the median spike ; if then their points are bent outwards 

 and backwards, it is clear that the larva will push itself forward, and 

 readily bore into any object opposed to it. The anterior stigmata 

 are pretty large ; they are on the sides of the upper part of the 

 second segment ; they are round, and bordered on the inner margin 

 by a semilunar chitinous band. Posterior stigmata forming two 

 small, irregular, porous, chitinous plates. Round the stigmata the 

 last segment bears numerous small, round chitinous plates, which give 

 it a punctured appearance. The larva has eleven segments, and ap- 

 pears naked ; there are some microscopic spines only in the funnel- 

 shaped pit of the mouth and on the margin of the lower lip. „~,<^, 



Second stage (duration very short, at the utmost one month. 

 This form appears from the end of January to the middle of February, 

 usually together with the first and third forms). — Larva at first 



