412 THORACIC GLANDS IN LAEV^ OF TJBICHOPTEEA. 



epiblastic invagination is still very shallow. Their nepliridial 

 significance, suggested already by their excretory function, is thus 

 supported by serious morphological considerations. 



The similarity o£ structure between the Malpighian nephridia 

 and the glands here noticed seems thus to plead in favour of the 

 nephridial character of the latter. 



No trace of segmentally repeated organs, be they coxal or 

 nephridial, has been hitherto detected, so far as I am aware, on 

 the thoracic segments of the Hexapoda. Even in the lowest 

 forms of insects (Thysanura), where remains of segmental organs, 

 probably coxal, may be detected on all the abdominal segments *, 

 BO trace whatever of such organs is known on the thoracic, with 

 the exception of the single " Bauchdriise " in the prothorax of 

 certain Lepidoptera, and some scent-glands in certain Hemiptera. 

 It is thus worthy of remark that in Trichoptera each of the 

 thoracic segments of the larva may possess a gland, and in its 

 segmental repetition they reveal an ancestral character that 

 could not be affixed with security to the single " Bauchdriise " or 

 to the scent-glands. There is thus possibly no segment of the 

 Hexapod body left that can be said to be completely wanting in 

 traces of segmental organs in some member of the group. 



Conclusion. 



1. In the larval Trichoptera each of the thoracic segments may 

 be provided with more or less complex glandular organs more 

 nearly representing nephridia than the coxal glands of Annelids 

 and Peripatus. By the discovery of these it may now be said 

 that : 



2. In the Hexapoda remains of segmentally disposed glandular 

 organs, be they coxal or nephridial, are known for the whole 

 length of the body, from the mandibular to the posterior abdo- 

 minal segments. 



* Oudemans, ' Beitrage zur Kenntniss des Thysanurae und Collembolse,' 

 Berlin, 1888. 



