ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 593 



sarasinorum Karsch) living in a sponge-like nest of ramified canals, often 

 attached to branches of trees or to leaves of the prickly pear. The 

 number in a nest varies from 40-100, males and females usually in the 

 proportion of 7 to 1, though sometimes the females are less numerous. 

 A number often co-operate to achieve a definite end, e.g. securing victims ; 

 and food is shared without quarrel. The absence of much disparity in 

 size and colour between the sexes, the friendly and communal living of 

 the males and females in the same nest, and the happy, almost affec- 

 tionate relation that subsists between the sexes, indicate a high order of 

 development. The maternal feeling for the offspring verges almost on 

 self sacrifice. 



In an appendix it is noted by Mr. N. Banks that the author seems 

 to be unaware of other records of social spiders, e.g. Stegodyphus gregalis 

 from South Africa (0. Pickard Cambridge), Uloborus republicanus 

 from Venezuela (Simon). 



<• Crustacea. 



Metamorphoses of Hermit Crab.* — Millett T. Thompson has made 

 .a study of this interesting life-history. The adult Eiipagurus has a 

 thorough-going dextral asymmetry. Scarcely any system of organs in 

 the body escapes some modification. However, with the exception of 

 the flexor muscles and arteries of the abdomen, the homologies with 

 other Decapods are clear. But the diagonal muscle bands and the 

 peculiar division of the superior abdominal artery into two trunks are 

 interpretable only from a study of the larva. The muscles are then 

 shown to be a greatly degenerated loop-enveloping system, from which 

 the transversalis muscle has been lost. The arteries resolve themselves 

 into supra-abdominal and a new vessel, primarily derived from the 

 second segmental artery of the right side, and probably peculiar to 

 Pagurids. 



The development is concentrated. There are four stages in the 

 zosea phase, the last of which is a metazoaBa. The post-zoffial or glau- 

 cothoe phase consists of one stage, which is macruran in general form 

 and from the first presents a mingling of adult and larval characters. 

 Details of this are given. 



The metamorphosis by which the structures attain the adult type 

 commences before a shell is taken, and the stimulus of a shell is not 

 necessary for its completion. But the shell is very important in affect- 

 ing the duration of metamorphoses and for the health of the animal. 

 The anatomical modifications that appear during the glaucothoe stage 

 are, with but one exception, uninfluenced by either the presence, absence, 

 •or form of the shell. The exception is found in the retention of rudi- 

 mentary pleopods on the right side of the body in the sixth stage, 

 though typically at this period appendages should be absent from 

 this side. 



There is evidence that hermit crabs show a preference for dextral 

 shells, and the author thinks there is a strong presumption in favour of 

 •the view that the asymmetry was, from the first, a result of life in dextrally 

 spiral shells. 



* Proc. Boston Soc. Nat. Hist., xxxi. (1903) received 1905, pp. 147-209 (7,pls.). 



