Claassen: Larva of a Cpilronomid. 399 



lies across the body of the nymph, but as it grows hxrger the 

 posterior end of (ho body doubles under, and later, when the larva 

 becomes full grown, the middle part of its body projects backward 

 over the abdomen of the nymph in the form of a letter U. When 

 ready to pupate the larva releases its hold at the head end and turns 

 back over the abdomen of the nymph. The pupa thus extends over 

 about half the abdomen of the host. Tlic transparent sheet of silk 

 invests the pupa as well as the larva. Just before the adult is 

 ready to emerge the pupa breaks through this investing membrane 

 and rises to the surface of the water, where the adult emerges in a 

 manner similar to that in other chironomids. 



That the larva is a parasite upon the nymph is apparent from 

 the following facts: First, the silk membrane completely sur- 

 rounds the larva. There is no opening in this membrane which 

 would make it possible to obtain food from the outside. Second, 

 an examination of the stomach contents of a number of larvae 

 failed to reveal the presence of any vegetable material, but did con- 

 tain animal matter, especially fat bodies. This fact was also borne 

 out in a study of cross sections of the larvse. Third, a study of 

 the head and mouth parts of the parasite reveal their reduced con- 

 dition. Tlie head is very small in proportion to the size of the body 

 and the mouth parts are much reduced. 



The European species of the genus Trissodadius, of which the 

 larvae are known, are all found as free living forms feeding upon 

 vegetable matter.* 



The reduced size of the head and mouthparts of Trissodadius 

 equitans indicate that this parasitic relationship has existed for a 

 long time. Whether the parasite ever becomes so injurious as to 

 kill its host the writer has not been able to determine. Another 

 question of interest is what happens to the parasite when the nymph 

 casts its skin. The life cycle of the parasite is either so short that 

 development is completed during a nymphal instar of the host, or 

 else the parasite must be able to detach itself from the cast skin 

 and reestablish itself upon the newly emerged nymph or upon an- 

 other individual, otherwise it must perish. 



There appears to be no relationship between the relative ages of 

 the host and parasite. Pupa? of the parasite were found upon 

 medium-sized nymphs, while, on the other hand, young larvse oc- 

 curred upon nymphs that were evidently in the last nymphal in- 

 star. 



*Barnard, K. H., in the Entomologist's Monthly Magazine, vol. 47:76-78, 1911, reports 

 the case of a chironomid larva (name not given) which is parasitic upon a fresh water snail, 

 Limnoea peregra. 



