OBSERVATIONS ON THE EMBRYOLOQY 



OF 



INSECTS AND ARACHNIDS. 



The important points to be determined in Insect embrj'ology are, the segement- 

 ation of the egg and formation of the blastoderm the origin of the embryo and 

 embryonic membranes the formation of the germinal layers metameric segement- 

 ation and all connected with it including number of appendages, nerve ganglia 

 and etc. 



The embryology of Arachnids, or at least of spiders, in some important par- 

 ticulars resembles the embryology of Insects. These points of likeness will be 

 brought out in the detailed description of the embryology of spiders which will be 

 given later. 



The Insects studied included representatives from the Lepidoptera, Coleoptera 

 and Orthoptera ; while a few incomplete observations were made on the embryology 

 of the Neuroptera and on the maturation of the ovum in Musca. The ova were 

 studied by means of sections. With opaque eggs the sectional method of study 

 certainly throws more light on important embryological points than mere super- 

 ficial observation. 



The eggs were hardened in corrosive sublimate and in Perenyi's fluid. The 

 chorion was punctured to admit hardening and staining fluids. After staining 

 they were passed through the various grades of alcohol and were then transferred 

 to chloroform they were then placed in a mixture of chloroform and parraffine, in 

 which they remained a shorter time. They were then embedded in paraffine and 

 were readily cut to any degree of thinness required 



