4-0 BULLETIN OF THE BUREAU OF FISHERIES. 



The labrum (fig. 39) is thin and but slightly developed compared to the labrum 

 in the Chironominse. It is furnished on its anterior border with several processes 

 apparently possessing sensory functions. These processes seem to be of more or less 

 specific value and may sometime be of use, as this group is lacking in really good larval 

 characters of systematic value. The chitinous processes (cp) may be homologous to 

 the lateral arms of the hypopharynx of the Chironominae. 



The head structure of Tanypus is quite unique, being developed for a special manner 

 of life, and the constant recurrence of this structure throughout the group, together 

 with the great similarity in the habits of these species, seems to abundantly justify 

 the placing of all the species in one group. From the ventral side of the head one is 

 able to distinguish longitudinally arranged muscles which are attached at one end to 

 the chitinous framework of the hypopharynx and at the other end to the posterior 

 border of the head. From the dorsal surface, however, one sees a very different mus- 

 cular arrangement. Here the muscles in the anterior part of the head radiate anterio- 

 laterad from the mid-dorsal line, and in the posterior part of the head they radiate 

 posterior-laterad from this same mid-dorsal line. Here in the center of the head is 

 an area which doubtless serves as a sort of pump and to which are attached long muscles 

 which radiate anteriorly and posteriorly. This pump is a structure present throughout 

 the subfamily so far as the author has observed. 



Another unique feature of the head is the presence of retractile antenna;, which 

 Meinert (1882) has figured and described in detail. He does not seem to have observed 

 their functional significance, however, but considers them only from the standpoint of 

 their anatomy and homology. It will, therefore, be sufficient to state that the 

 antenna; are withdrawn into the head capsule itself where there are special chitinous 

 sheaths to receive them. They are withdrawn by special well-developed muscles and 

 are said to be extended by blood pressure. They are of great functional importance 

 in that they enable the larvae to actually measure the distance from their prey. A few 

 easily made observations enable one to see how constantly they are used. The larvae 

 prowl about with their antennae partially extended, and upon encountering an active 

 object they withdraw them as they approach, thus keeping in touch until near enough 

 to seize the object. 



FEEDING HABITS. 



The larvae are all predacious as far as the author has been able to determine, 

 although it is very difficult to actually observe them feeding. Numerous studies of 

 the stomach contents of the larvae have shown such an array of diatoms and desmids 

 as to entirely mislead one looking for proof of their predacious habits. Meinert (1886) 

 states that he has observed a living Simocephalus in the intestine of a Tanypus larva, 

 while Miall and Hammond (1900) have apparently observed indubitable evidence that 

 they were predacious on bloodworms from the presence of the heads of these larvae in 

 their stomachs. 



It was not, however, until the author had starved a Tanypus carneus larva for a 

 week that he was able to observe the actual feeding habits. This larva when put in a 

 dish containing a number of large Cyprididae would apparently strike at them when they 

 came in contact with its head. The striking seemed to be a more or less involuntary 

 reaction, for when the nature and size of these crustaceans were discovered they were 



