OLDEST KNOWN INSECT-LARVA. 437 



cally with recurved hooks. The objections to considering this as the most nearly allied 

 group are the considerable size of the legs even when least developed, the great size of 

 the head, which is at least as large as the segments behind, and the slight differentiation 

 of the prothoracic segment shown at least in its larger size. 



I had reached the conclusion that upon the whole we might look upon the Sialidae at 

 the group of insects to which Mormolucoides was the most nearly allied (though still 

 regarding the conclusion as provisional) when it received a curious support from an 

 unexpected quarter — the internal structure of the larva. I have said that several spec- 

 imens of Mormolucoides showed traces of the alimentary canal, and that in two of them 

 (figs. 2, 11) in the posterior part of the body it doubled twice upon itself, covering with 

 its triplication the sixth abdominal segment anil parts of others, indicating a convolution 

 of the small intestine. Looking at the published accounts and figures of the internal 

 organs of the larvae of the three groups of JSTeuroptera we have been discussing, I find 

 that the digestive tract, so far as known, is invariably straight and simple in both Per- 

 lidae and Ephemeridae, while a triplication of the small intestine is not unknown in Sial- 

 idae, being distinctly figured and described by Leidy in Corydalis cornutus, 1 where it 

 covers the fifth abdominal segment, or the one next in advance of that in which we have 

 found it in Mormolucoides. The only other figure of the digestive tract of a Sialid larva, 

 which I have found, is that of Sialis lutarius published in the same year by Dufouiv 

 where it is figured as perfectly straight and described similarly as "droit comme celui de 

 1'insecte aile." Several species in their perfect state, in groups closely allied to the Sial- 

 idae and sometimes placed with them, such as Panorpa, have a similar triplication of the 

 small intestine, and it is also found in the larva of Myrmeleon as figured by Dufouiv 1 

 These seem to be fair corroborations of the conclusion independently reached, that Mor- 

 molucoides is probably the larva of a Sialidan neuropteron. It has special interest from 

 the fact that it is the oldest known insect larva. 



EXPLANATION OF PLATE 45. 



All Ihe figures represent Mormolucoides articulatus, and all but fig-. 3 were drawn by J. Henry Blake. Fig. 8 is natural 

 sfze ; fig. 3 enlarged about 5 diameters ; the others enlarged 3 diameters. 



Fig. 1. A specimen from Montague, Mass., collected by Prof. O. C. Marsh and in the Peabody Museum of Yale Col- 

 lege. The head is smaller than usual. 



F'ig. 2. From the same place and collection as the last and on the same slab as fig. 1G. Although imperfect, the head 

 and first thoracic segment wanting, it shows remarkably a sharp median groove, which can be nothing else than the diges- 

 tive tract, with the indication of its twice doubling on itself at the end of the fifth and base of the seventh segments. A 

 slight indication of one of tin' anal styles is also .-ecu on the last segment. 



Fig. 3. The head and fir>t thoracic segment of a specimen in the Vale College Museum, as drawn, many years ago. 

 by S. II. Scudder. It shows the apparent division of the head into two segments, then supposed to be head ami first thor- 

 acic segments. 



Fig. 4. Specimen from Montague, Mass., collected by Professor Marsh and now in Ihe Peabody Museum at New 

 Haven. It shows a head of unusual breadth, basal abdominal segments which are larger than (he thoracic, and slight in- 

 dications of the lateral appendages of the abdomen. 



Fig. ■"). Specimens from Turner's Falls, Mass., marked No. 1,405 in the Shepard collection of Amherst College. Figs. 

 11 and 12 are on the same slab. This specimen shows well the lateral marks of the thoracic segments interpreted as possi- 

 bly legs, a well marked differentiation of the thoracic and abdominal segments, and an unusually uniform breadth in the 

 latter. 



Fig. C. This specimen appears to be the original type of Mormolucoides articulatus. It is on the same slab with tig. 

 ]."., marked as coming from the Horse Race, Gill, and numbered }j in the lanherst College collection. There is not m 



1 Mem. Amer. Acad., iv, 1G2-168, L'l. 1, 2: 1848). -Ann. Sc. Nat. (3), i\, 91 99, PI. 1 (ISIS). 



J Mem. Saw Etrang. lead. Sc, vn. l'l. 12, ligs. 175, 177 (1811). 



