l6 BULLETIN OF THE BUREAU OF FISHERIES. 



succession indicates that the silk hardens very quickly on contact with the water. 

 The quickness with which the silk hardens determines the speed at which the larva 

 must work in order to spin silk of a given thickness. Hence, the thinner the structure 

 the greater the speed required, because of the greater surface relative to the volume 

 exposed. Thus it appears that the very rapid movements of the larvae are dictated 

 by considerations of economy in the silk used. 



RELATED FORMS. 



Goetghebuer (1911) in a special examination of the external structures of the 

 larvae of the genus Chironomus established three groups, as follows: 



Group I. — Containing those species possessing two pairs of branching filaments 

 on the eleventh segment; a thickened oval area on the labrum; an epipharyngeal 

 comb composed of a row of regular teeth; the antennae with five segments; and the 

 abdominal segments of the pupa without spinose protuberances. 



Group II. — Branchial filaments of the eleventh segment lacking; the median 

 anterior piece of the labrum simple without the thickened oval area; the comb of the 

 epipharynx not composed of a regular row of teeth; the antennae with five segments 

 without Lauterborn's organs; and the pupa without spinose protuberances. 



• Group III. — Agrees with Group II except in the presence of small granulations 

 on the labrum of the larva and the presence of spinose protuberances on the posterior 

 abdominal segments of the pupa. 



The specimens upon which the last two groups were founded all live in the paren- 

 chyma of submerged leaves of numerous aquatic plants and are as follows : Chironomus 

 sparganii Kieffer, C. viridis Macquert, C. niverpennis Fabricus, C. tendens Fabricus, 

 and C. dispar Meigen. The list of plants in which these larvae were found as given 

 by Goetghebuer is as follows: Straiioies aloides, Sparganium ramosum, Butomus umbel- 

 latus, and Alisma plantago. 



In addition to this list the author has bred Chironomus lobijerus Say, C. pedellus 

 Deger and Tanytarsus obediens Johannsen, from Sparganium stems, and Needham 

 (1908) reports Chironomus albistria Walker from Nymphaea stems. While, of course, 

 only the bred specimens have actually been observed to build conical feeding nets, 

 yet the similarity of their external structures and the nature of their habitat give a 

 considerable justification for including them in this group, especially when it is observed 

 that Tanytarsus obediens, a member of another genus, possesses this habit. 



A bit of information regarding the similarity of the larvae of Chironomus sparganii 

 Kieffer is contained in a paper by Willem (1908). He finds the uniform punctations 

 of the abdominal tergites, the posterior teeth of the lateral plate of the eighth segment, 

 and especially the peculiar process carried by certain abdominal segments would 

 suggest C. lobiferus Say, the description of which was found in Johannsen's monograph. 

 He finds his most striking difference in the fact that Johannsen says that these processes 

 occur on all the segments, while he finds them on segments two to six only. Upon 

 examining his own material the author finds this to be also true for C. lobiferus Say, 

 as well as C. sparganii. Dr. O. A. Johannsen has also observed the author's material 

 and agrees with him in the identification of this species. While it is not known how 

 great weight this observation had with Kieffer in establishing the species C. sparganii, 



