ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 407 



Comparative Biology of Necrophagous and Coprophagous Dip- 

 terous Larvae.* — Baron Osten-Sacken has a report on Mr. Portchinski's 

 observations on the life-history of various dipterous larvae. Referring 

 to the well-known fact that the larvae of various widely separated 

 species can scarcely be distinguished from one another, he points out 

 that this is a result of adaptation to their modes of life. The larvae of 

 Calb'phora erythrocephala, Lucilia csesar (which are Muscinae), and 

 Cynomyia mortuorum, which is a Sarcophaginid, are almost indistinguish- 

 able. The coprophagous larvae, which are found in very various 

 families, all show a tendency to shorten as much as possible the period 

 of development, and in many cases they are viviparous. The compara- 

 tive ease with which the course of development may be modified is 

 shown by Musca corvina ; in the north of Russia this species lays 

 twenty-four eggs, and the larvae omit the second stage of development ; 

 in the south of Russia the same species has the same history in spring 

 only ; towards the end of spring and in summer it lays only a single 

 very large egg, which, on extrusion, passes at once into the third stage- 

 All the various modes of development, which result in as rapid an 

 acquirement as possible of the imaginal stage, are regarded by Mr. 

 Portchinski as the consequence of the coprophagous mode of life of the 

 larvae. The large number of such forms are found together on food- 

 areas which are often small, and this causes the animals to complete 

 their developmental stage as rapidly as possible. With this is con- 

 nected a small degree of fertility. 



That Musca domestica (the common housefly) should afford an ex- 

 ception by laying a large quantity of eggs (120-160), and by its larvae 

 passing through all three stages, may be explained by its having 

 become a domesticated animal, which is not exposed to the same struggle 

 for existence as are its allies. 



Organization of Brain of Somomya erythrocephala.t — Dr. J. Cuccati 

 has a contribution to our knowledge of the structure of the brain in 

 insects. In the brain of Somomya he finds that the olfactory-optic- 

 bundle of Bellonci is present, together with the bundle which connects 

 the antennary swellings with the fibrous plexiform substance of the 

 head of the fungiform body ; there, too, is the crossed olfactory-optic- 

 bundle of the same author. The antennary swellings are connected 

 with one another by two large and by intermediate smaller commissures. 

 The antennary nerves consist of fine outer and larger inner fibres ; they 

 are connected by nerve- fibres with the central stalk, and with the motor 

 nerves of the labium. The optic swellings are likewise connected by 

 commissures with one another. They give off a crossed bundle, the 

 fibres of which pass into two plexiform masses ; they are directly con- 

 nected with the anterior cerebral masses and with the hinder masses of 

 the cerebral spheres. 



In the brain there are a larger number of commissures placed in 

 different planes ; there are also crossed bundles, which arise from the 

 cells in the median line, and these send off fibres in the direction of 

 the optic swelling. As in the Orthoptera there are two bundles, one of 

 which arises from cells and the other from the plexiform mass ; the 

 former serves to supply the proboscis, and the latter passes into the 



* Naturforscher, xxi. (1888) pp. 66-7. 



t Zeitschr. f. Wiss. Zool„ xlvi. (1888) pp. 240-69 (2 pis.). 



