ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 785 



Malpighian tubules ; ' then the area bounded by them becomes de- 

 pressed, and will give rise to the rectum. 



g. Silk-glands, dc. — A little behind the point where the second 

 maxilhe will be formed, two fossae appear, which are directed back- 

 wards, and ultimately extend through nearly the whole extent of the 

 body ; these are the silk-glands, and the two pores later on unite to 

 form a single median opening. The salivary glands are formed as 

 ectodermic invaginations just in front of the mandibles ; each divides 

 into a longitudinal and a transverse branch. The two transverse 

 branches unite. A third pair of pits appear between the first and 

 second maxilla}, but they soon disappear. 



h. Ccelom. — As the stomodaBum increases in length the yolk dis- 

 appears before it, and leaves a space filled w T ith liquid, partly occupied 

 by the oesophagus and mesoderm. The posterior portion of the yolk 

 behaves in the same way, and the yolk becomes concentrated round 

 the future stomach or mesentcron. The mesoderm then divides into 

 two layers, which are in contact dorsally, but separate elsewhere. 

 No segmentation of the ccelom was observed, such as is described by 

 Tichomiroff. 



i. Dorsal vessel. — Along the line where the two layers of mesoderm 

 meet dorsally, the dorsal vessel is formed ; corpuscles appear before 

 the proper walls arc formed ; they arise from mesoderm, and not, as 

 Dohrn has described, from the yolk. > 



h. Genital organs. — Two solid cords of cells, without connection 

 with one another, extend from the fourth to the eighth abdominal 

 segment ; these are placed at the junction of the two mesodcrmic 

 layers, outside the dorsal vessel, and give rise to the genital organs. 



I. Lining of the middle intestine. — The stomach or mesenteron is 

 lined entirely by entoderm, which has already been described as at 

 first forming a roof to an internal cavity ; the sides bend round, and 

 meet on the ventral surface to form a tube. 



m. Appendages, dc. — The procephalic lobe appears as an unpaired 

 projection of ectoderm and mesoderm at the anterior extremity ; it, 

 later on, bends downwards so as to form the upper lip. 



The antenna} appear simultaneously with the buccal appendages : 

 of the latter there are four pairs, of which the first pair totally dis- 

 appears; while the rest form the mandibles and the two pairs of 

 maxilla). The thoracic appendages arise one after the other. 



The abdomen, as a rule, carries no appendage ; but in one or two 

 instances Prof. Grassi saw paired processes on the last segment, and 

 on that carrying the tenth pair of stigmata; these soon, however, 

 disappeared. 



Biitschli appears to have mistaken the prominences formed by the 

 deep intersegmental grooves for rudimental abdominal appendages. 



II. General part. — The development of the bee may serve as a 

 type, up to a certain point, of the development of insects generally, 

 although the Hymenoptera seem to be the highest of the insects, and 

 the bees the most advanced of this order. 



a. Formation of the blastoderm. — The segmentation of the egg is 

 very similar in the bee to that observed by Biitschli in the Lepidoptera, 

 Ser. 2.— Vol. VI 3 F 



