which inhabit the Tissue of Spongilla Fluviatilis. 107 



with which it and the sides of the body are furnished, are very 

 greatly elongated. On tlie underside (fig. 2) each of the seven 

 basal segments of the abdomen is furnished on each side with a 

 long and slender, flattened filament, destitute of ciliae, and which is 

 directed, first, inwardly, and then backwards. These filaments, 

 fourteen in number, are articulated,* and have much the appear- 

 ance of weak legs, but they are evidently organs of respiration, 

 one or two slender tubes being easily perceivable running through 

 them, and terminating in a point. The articulations do not appear 

 of equal size throughout these appendages (fig. 10, 11, 12). 

 The eighth abdominal segment is destitute of these filaments, but 

 is furnished with larger setigerous lateral tubercles than the pre- 

 ceding joints, and the terminal segment is small and simple, in one 

 specimen it was much larger and conical. Each of the abdominal 

 segments is furnished with a pair of leathery darker coloured 

 patches, emitting from its posterior margin three long setaj (fig. 

 6, 7). ^ 



The inquiry as to the relations of this insect and the order and 

 family to which it belongs, is attended with great difficulty, from 

 the anomalous characters which it possesses. 



Its small size, green colour, structure of the mouth, and form 

 of the legs seem to indicate a relation with such families as the 

 Aphidce and Coccidce, which possess species which never acquire 

 wings. Coccus, as I have discovered, possesses a mouth, con- 

 sisting of four exceedingly long and slender setas, although 

 Mr, Curtis, in this month's number of his British Entomology, 

 states that it consists only of three setae ; but these insects are 

 aquatic, and are furnished with external elongated organs of 

 respiration, which exist in no known imago. If regarded, then, as 

 larvae, the question is still more perplexing ; the general struc- 

 ture of the insect, and the particular structure of its mouth, 

 prevents it from being considered as Coleopterous, Orthopterous, 

 Lepidopterous, Hymenopterous, Strepsipterous, or Dipterous. 

 It will not enter, as a larva, into any Hemipterous or Homopterous 

 family, so that there only remains the Neuroi^itera, amongst which 

 we are to trace its relations ; and it is in this order that we find 

 external organs of respiration in the aquatic larvae. But the 

 structure of the mouth prevents our associating it with any group 

 of which the larvae are aquatic, and known. The Perlulce, Ephe- 

 meridce, LibeUuUdce, Sialidce, and the order Trichoptera, are well 

 known in the larva state, whilst Boreus and Panorpa are the only 



* The respiratory filaments of Sialis are also articulated, being the only known 

 instance, according to M. Pictet, in which such a structure has been observed to 

 exist. No known Ephemerideous larva is destitute of the three anal filaments. 



