ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 43 



Many nests containing- living larvae were found on the young saplings of 

 a pine forest at Arcachon, and in all cases the branches near the nest were 

 matted with the threads secreted by the larvae. Below the nest threads 

 were rare, and only a few (none of which reached the ground) were found 

 i >n the trunks. The threads gave no evidence that leaving the nest and 

 returning to it was a frequent habit. Many experiments were made 

 with the thread formed by a procession on the march. The general 

 result of these was to show that the thread is of very slight importance 

 either in the formation of a procession, or in maintaining its integrity. 

 The thread forms the nest in the tree and the cocoon in the pupa state, 

 but the reason why it should continue to be secreted while the larvae 

 tire feeding or away from the nest remains obscure, unless it may be 

 regarded as an excretion. Experiments in regard to leadership showed 

 that the same leader took the head of the procession in about 50 p.c. of 

 cases, when it was re-formed after either natural or artificial massing. It 

 seems certain that contact between the larvae is of much importance, and 

 that, though there is no permanent leadership, the leader for the time 

 being does determine the behaviour of the procession, because all its 

 members endeavour to maintain a head-to-tail contact. Mass formation 

 is always, and burrowing frequently, begun by the leader. The observer 

 experienced no irritation from handling the caterpillars, and believes 

 with Edwards, that the sensibility to the glandular hairs varies with the 

 individual. 



Spermatogenesis in Lepidoptera.* — Margaret Harris Cook has 

 studied Callosamia promothea and some other types. A careful examina- 

 tion of the chromatin elements show's that one acts differently from the 

 others during a certain period in the development of the germ-cells. It 

 is distinguished from all other cell -structures by its staining reaction, its 

 precocious division, and its close association with a plasmosome ; while 

 later it shows likeness to the other chromosomes in form, valence, and 

 division ; such behaviour makes it necessary to interpret this, as other 

 workers have done, as an equal pair of idiochromosomes representing 

 different characters from those of the other chromosomes, and expressing 

 by their peculiar behaviour a masked dimorphism. 



The following facts are in favour of the theory of the individuality 

 of the chromosomes : the number remains the same from generation to 

 generation ; they are seen in maturation-divisions to be formed of pairs 

 of equal size ; in smear preparations the boundaries can be traced, and 

 the chromosomes never entirely lose their continuity during the growth 

 stage, and at least one of the chromatin elements shows marked pecu- 

 liarity in its behaviour, and can therefore be traced throughout the 

 growth period. These facts show that Lepidoptera, like the other 

 Insect orders, may be brought into harmony with recent cytological work. 

 A summary of the detailed observations is given. 



New Flea from Jerboa. f—Alfons Dampf gives a full description of 

 Mesopsylla eucta g.etsp.n. from Alactagajaculus, and makes comparative 

 tes on Palseopsylla Wagner, and other fleas. 



* Proc. Acad. Nat. Sci. Philadelphia, 1910, pp. 294-327 (6 pis.), 

 t Zool. Jahrb., 1910, Suppl. 12, Heft 3, pp. G09-64 (34 figs.). 



