THE LIFE-HISTOKY OF A LEl'lDOl'TEKOUS JlSSEcT. 215 



ment, and increases somewhat in size ; when the infolding is complete, 

 that is, when the outfolded edges of the blastoderm cells have met and 

 closed over the whole ventral plate, the latter is about as long as the 

 egg, but so curved as only to reach about three-fourths way to the to}). 

 It will be seen that the embryo has now two layers of cells outside of it, 

 one extending all around, and the other only across the outside face of 

 the ventral plate ; between these two layers the yolk penetrates freely. 

 Great confusion exists as to the nomenclature of the membranes, but I 

 prefer to follow Balfour in this matter, and designate the inner as the 

 amnion, and the outer as the serous membrane, though the reverse is 

 perha^DS the more common practice. From this history of their forma- 

 tion it is evident, that both layers and the ventral plate are modified 

 blastoderm-cells, and that the membranes can in no sense be called 

 moultings of the ventral plate." 



11. On THE EMBRYONIC DEVELOPMENT OF ToKTKIX FERRUGANA. — I 



have recently been studying the embryonic development of Tortrix ferrn- 

 gana. It appears certain that there are in its embryo four distinct cephalic 

 segments, which in the early stages of embryonic development are large, 

 (compared with the other segments which are developed later), and are 

 made still more distinct by the possession of buds or processes. As 

 development goes on, these four segments get welded together, and 

 become not only proportionately, but absolutely smaller than at first. 

 When the abdominal segments are in course of development, there 

 certainly appear to be eleven of them. The three thoracic segments are, 

 in the early stages of development, large and almost circular, and the 

 next segment (1st abdominal) is of the same character, looking at this 

 time much more like a thoracic than an abdominal segment, though it 

 has, of course, no appendages. The eye-sj^ots in this species are re- 

 markably conspicuous as two reddish jjatches, and become apparent at 

 about the same time that the abdominal segments first show. As 

 development proceeds, the cells of the develo2)ing T. ferrugana appear 

 to be stained here and there with red patches, esj)ecially along the 

 ventral area of the alimentary canal, but differently distributed in 

 different examples ; these afterwards spread over the whole of the 

 embryo. Dr. Chapman suggests that this colour is 23robably connected 

 with the larval skin. "When the embryo begins to show traces of 

 segmentation, the thoracic segments are seen to develop three pairs of 

 jointed buds or legs. At this time the embryo occujjies a soiuewhat 

 curved position, with the head slightly bent round towards the anal 

 extremity, but with the legs outside, i.e., the larva is bent back on itself 

 so as to form a curve agreeing roughly with the curvature of the shell, 

 with what afterwards becomes the ventral surface of the larva outside, 

 and the dorsum towards the centre. The embryo then gradually 

 changes its position, the anal segment curling round and being })us]ied 

 by the growth of the preceding abdominal segments, slowly up tlic 

 ventral surface of the larva, whilst the dorsum gets j)ushed out, as it 

 were, towards the centre of the egg. During this process the embryo 

 becomes shaped something like the letter S, the movement continuing 

 until a complete reversal of the embryo has been effected ; the next 

 stage is that in which the head and anus are in contact, each half run- 

 ning almost parallel, and this again is followed by an almost circular 

 position, in which the dorsal area is outside, and the ventral surface 

 (with the legs) on the inside. The head diuing all this time scarcely 



