Packard.] 



14 J June 15, 



tip of the abdomen is deeply cleft by the median furrow of the body. 

 The rudimentary mandibles and 1st maxillae are distinct; the ceph- 

 alic lobes appear very distinct, and the antennae are nearly twice as 

 large as the legs. I was unable, after careful and repeated en- 

 deavors, to discover at this or any other period, any traces of the 2d 

 maxillae (labium) though they may be found on more careful examin- 

 ation hereafter, as they are present in a very rudimentary form in 

 the adults, and are large and well developed in the Lepismatidae. 



A later period still (Fig. 3, 3a) is characterized by the differen- 

 tiation of the head as a distinct region of the body; the posterior 

 portion, including the mandibular and 1st maxillary segments, unit- 

 ing with the cephalic lobes, in which the eyes (each now consisting 

 of eight ocelli) are situated. The antennae are now of much the 

 same shape as in the larva, while the epicranium, clypeus and 

 labrum are differentiated, and the "spring" is fully formed, con- 

 sisting of a pair of finger-shaped, three jointed appendages, the 

 basal joints consolidated into a single tubercle, from which the ex- 

 tremities diverge. 



Another well marked stage, i.e., just previous to the hatching of 

 the embryo, is signalized by the mandibles and 1st maxillae becoming 

 acute, closely appressed to one another and to the under side of the 

 head, and withdrawn within the head, so that the mouth is some- 

 what tubular, as it appears in a front view of the head. At this 

 period, also, the absence of any apparent traces of a labium is 

 worthy of notice. 



The embryo throws off the chorion and amnion in a moment, and 

 the larva is very active in its movements. The larva is white, be- 

 coming after a second moult of a purplish hue, while the adults are 

 snuff brown. The larva is much shorter and thicker than the adult, 

 and the spring is very short and stout, while the head is much 

 rounded, and the antennae are short, and thick, and very large. In 

 fact the larva repeats the general form of Podura, Aclwrutes and 

 Lipura, while the adult is more closely allied to Degeeria. The 

 species, which is undescribed, is named Isotoma Walkerii, and belongs 

 to Nicolet's first section of the genus, of which the European /. 

 glacialis is a type. 



The development of this insect is throughout very similar to that 

 of the Phryganeidae ; the germ, as in that neuropterous family, be- 

 ing developed on the outside of the yolk. The parietal membrane 



