548 SUMMARY OF CURRENT RESEARCHES RELATING TO 



phototactic ; negatively geotactic when in need of oxygen, and positively 

 so when supplied with it, but mechanical stimulation interferes some- 

 what with the character of geotactic responses. Numerous other results 

 are recorded, and it is concluded that with increased knowledge of the 

 animal its actions become the more referable to external stimuli. 

 Nevertheless these responses are constantly modified from within the 

 organism itself by the tonus, or physiological condition, in which the 

 animal chances to be at the time. 



Arthropoda. 

 o. Insecta. 



Locomotor Cuticular Outgrowths in Insect Larvae.* — W. Leisewitz 

 has made a detailed study of (1) undifferentiated hairs, (2) spines result- 

 ing from the coalescence of groups of hairs, and fixed to basal plates 

 which may grow into cones, (3) tubercles which result from further 

 growth and, it may be, fusion of basal cones with reduction of the spines, 

 and (4) setse which are shorter and thicker than the hairs, and are often 

 curved and expanded. Of course there are intermediate forms between 

 hairs and spines, spines and tubercles, hairs and setae. 



The cuticular processes in burrowing larvaa are disposed in relation 

 to locomotor efficiency. Their particular character is adapted to the 

 material in which the larvas burrow. Their size is correlated with the 

 degree of activity. They always point in a direction opposite to that of 

 locomotion. They afford fine examples of convergence, for the cuticular 

 processes of unrelated larvas living in similar conditions are often closely 

 alike. 



Morphology of Insect Head.f — K. W. Verhoeff has made a detailed 

 study of the head, especially in Thysanura and Dermaptera. He dis- 

 tinguishes three groups of " segments " — 



(a) Those laid down in the young germinal streak and well developed 

 in the older embryo, e.g. the antennary segments, the 3 jaw-segments, 

 the 3 limb-bearing thoracic segments. 



(b) Those laid down in the young germinal streak, but less distinct 

 or vestigial in the older embryo, e.g. the praamandibular segment. 



(c) Those which are as such indistinct in the young germinal streak, 

 but distinct in the post-embryonic stages, e.g. the 3 segments of the 

 protocephalon and the primitive intermediary segments (Urzwischen- 

 segmente) on the thorax and abdomen. 



Of the 7-8 segments in the head of Thysanura and Dermaptera, 

 4 belong to group {a), 1-2 to group (b), and 3 to group (c). 



He gives an account of these segments and their adult representa- 

 tion : viz. the labral-, clypeopharyngeal-, fronto-ocellar-, antennary-, 

 mandibular-, maxillipod-, and labiopod-segments. 



Abdominal Gland-Pockets in Insects.:}: — R. Oettinger gives an 

 account of the structure and relations, including certain histological 



* Ueber Chitinose Fortbewegungs-apparate einiger (insbesondere fussloser) 

 Insektenlarven, Munchen, 1906, 143 pp., 46 figs. See also Zool. Zentralbl., 

 xiii. (1906) pp. 376-9. 



t Nova Acta k. Leopold-Carol. Deutscb. Akad. Nat., lxxxiv. (1905) pp. 1-144 

 (8 Pis.). % Zool. Anzeig., xxx. (1906) pp. 338-49 (9 figs.). 



