200 SUMMARY OF CURRENT RESEARCHES RELATING TO 



there is a " breaking-joint," where the leg, if injured, can be thrown off. 

 The exposed surface left is covered by a thin cuticular membrane with 

 a small central hole, through which the nerve and blood-vessels of the 

 leg passed. If the leg be injured outside of the breaking-joint, except 

 near the tip, it is thrown off at the breaking-joint. The special pro- 

 blems which Morgan has studied are two : — (a) If the leg is cut off 

 proximal to the breaking-joint, will a new leg develope ? and (6) If the 

 leg is cut off distal to the breaking-joini, and can be prevented from 

 being thrown off at the joint, will regeneration take place from the ex- 

 posed end ? 



Under ordinary conditions of life, it seems almost impossible that a 

 leg should be broken off proximal to the breaking-joint, yet if it be cut 

 off in that region there is regeneration. Under ordinary circumstances, 

 if a leg is injured distal to the breaking-joint, the leg is thrown off at 

 the base, yet regeneration was observed from the cut end of a limb ex- 

 cised outside of the breaking-j >int. These facts seem to Prof. Morgan 

 to show in the clearest way that there is no relation between the regene- 

 ration of the leg and its liability to injury, but " perhaps a lively 

 imagination may find some way of reconciling these facts with the 

 popular dogma." [ Why should Weismann's interpretation be called a 

 dogma ?] 



Eegeneration takes place more quickly from the breaking-joint than 

 from inside or outside of it ; i.e. the conditions are more favourable for 

 regeneration at the joint than elsewhere. When the distal segment is 

 cut off, the regeneration takes place beneath the old surface, and this 

 might be regarded as the result of a process of adaptation ; but the author 

 would expect to find the explanation rather in the fact that the structure 

 of the end of the leg is different from that of its base. The small fourth 

 and fifth thoracic limbs, which do not seem to be often (if ever) injured, 

 regenerate readily. The terminal abdominal appendages regenerate very 

 quickly and quite normally, — while Weismann suggested that those of an 

 ancestral type might be expected. 



Eyes of Crustacea.* — Prof. G. W. Parker has studied the photo- 

 mechanical changes in the retinal pigment of Gammarus ornatus Milne- 

 Edwards. He finds that the changes are limited to the black pigment 

 of the middle and proximal portions of the retinular cells. In light the 

 abundant pigment of the middle part of these cells surrounds the rhab- 

 dome with a black sheath, while the proximal portion of the cells contains 

 scattered grains of pigment only, except for masses of pigment near the 

 nucleus. In the dark these conditions are reversed, and the absenco of 

 pigment round the rhabdome exposes the accessory pigment-cells, which 

 may have some reflecting function. No changes occur in the distal parts 

 of the retinal cells, and in this respect the eye of Gammarus is physio- 

 logically simpler than those of Decapods. 



Monograph, on Alpheidae-f — M. H. Coutiere publishes the first part 

 of an elaborate memoir on this subject. It comprises a historical survey, 

 an account of the internal and external morphology, a description of the 

 larval forms, with chapters on bionomics and phylogenetic relations. 



* Bull. Mus. Conip. Zool. Harvard, xxxv. (1899) pp. 143-8 (1 pi.). 



t Ann. Sci. Nat. (Zool), ix. (1899) pp. 1-559 (6 pis. and 409 figs, in text). 



