ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 193 



The means of over-sea dispersal are discussed. Young spiders of 

 nearly, if not quite, all families are more or less given to " ballooning." 

 Ocean drift may also aid, and many spiders are carried as stowaways on 

 ships. 



f- Crustacea. 



Regeneration of Limbs in Crustaceans.* — J. H. Paul gives an 

 account of a series of observations and experiments on tlie regeneration 

 of the legs of decapod Crustacea from the pre-formed breaking plane. 

 Homarns vulgaris, Eupagurus hernhardus, and Garciiias msetias were 

 taken as species typifying the process. All these form limb-buds or 

 papilla? in the process of limb regeneration. These papillas are covered 

 with a chitinous envelope, and their outer form and size are adaptations 

 to' the requirements of the animal. The papilla has very complete 

 sensory innervation, and this must provide for its protection by its 

 possessor. As it has no calcareous outer coating it is able to increase 

 in size, unlike the animal as a whole. The papilla of the lobster is 

 straight, that of the hermit-crab curved, while the shore-crab has a 

 papilla which may be folded on itself three times. Valvular action of 

 the diaphragm at the breaking plane plays a greater part in the 

 stopping of haemorrhage after self -amputation than clotting does ; and 

 the dilatation of small vessels which pass beneath the epidermis detaches 

 a layer of ceils. This layer of epidermis proliferates from its free edges 

 to form the new limb. A new diaphragm is the first structure laid 

 down, and differentiation takes place from the base outward. Muscle 

 arises at the growing tip from cells proliferated from the old epidermis 

 (an ectodermal structure), and the nerve grows outwards from the torn 

 end by cell proliferation. Muscle-fibres are anatomically complete 

 immediately before moulting. The fi brills are cross-striated and 

 enclosed in a sarcolemma, but full functional activity does not come till 

 several days after moulting ; it begins with slow, rhythmic movements. 

 Sarcoplasm seems to be less abundant than in the normal fibre. When 

 moulting occurs, the papilla is at once expanded to several times its 

 previous size by valvular action, and the epidermis, previously com- 

 posed of several layers of cells, now thins to a single layer, as is seen in 

 the normal limb. 



Some new points on autotomy among the decapod Crustacea are 

 set forth in another paper by the same investigator.f He finds that 

 autotomy of the walking-legs in the lobster and its allies is not a simple 

 tearing at the third f joint, as has often been stated, but is the result 

 of a pluri-segmental reflex, which, among other things, causes great 

 weakening of the limb at the central end of the third podomere along a 

 groove running partly round the limb at this point. The weakening is 

 due to a muscle — described and figured — inserted by a small tendon 

 into the ventral edge of the third segment. In the lobster, autotomy 

 of the walking-legs occurs about four seconds after nocuous stimulation. 

 In the Brachyura there is a latent period of only a fraction of a second. 



* Proc. Roy. Soc. Edin., xxxv. (1915) pp. 78-94 (4 pis.), 

 t Rep. Dove Mar. Lab., iv. (1915) pp. 44-52. 



