574 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(Astacus), and some other forms. There is an autonomic system con- 

 nected with the central system. Its function is to set the peristalsis 

 going and to control it. It consists of bipolar cells, eacli of which 

 gives off, on the one hand, a " receptor " process to the lumen of the 

 gut, and, on the other hand, an " effector " process which unites with 

 that of other cells in a plexus, from which fibres go to the muscles, 

 stimulating a terminal plexus. The nerve from the last abdominal 

 ganglion has very numerous ramifications in the musculature, where it 

 unites with the motor fibres. It regulates the automatic movement. 



Amphipods from North Side of Bay of Biscay.* — E. W. Sexton 

 discusses a number of Pleustidge and Eusiridas. In some species several 

 stages of development were found, which seem to prove conclusively that 

 not only do these animals become sexually mature before attaining their 

 full growth, but that, in both sexes, the secondary sexual characters 

 undergo considerable modification after sexual maturity is reached, the 

 character most affected being the second gnathopod. 



Sexual dimorphism is well illustrated in the collection, the second 

 gnathopod being the organ generally affected. One species, Symplenstes 

 grandimanus Chevreux displays a very unusual and marked type of 

 dimorphism, the side-plates and perasopods differing widely in the two 

 sexes, as well as both the gnathopods. 



The mouth-parts remain very constant, and form the safest basis for 

 specific distinctions. The antenna? and gnathopods, usually relied on, 

 are the parts most affected by sex and development. But it is in the 

 sensory equipment that most change is seen after sexual maturity is 

 reached : the ommatidia increase in number, the flagella of the antennae 

 increase in length, those of the male to a far greater degree than those 

 of the female, the calceoli, sensory filaments, and the like, develop in 

 both sexes, and the peduncles of the antennas in the male become 

 covered with masses or thick tufts of sensory filaments or sensory setae. 



Coagulation of Blood in Arthrostraca.f — John Tait has studied 

 this in Ligia oceanica. The explosive cells, discovered by Hardy in the 

 crayfish, have been studied in films of Isopod blood. They discharge 

 into the immediately surrounding plasma a material which either itself 

 coagulates or there induces coagulation in the portions of plasma reached 

 by it. In this way a little localized island of coagulation is formed 

 around each exploded corpuscle. These islands, once formed, are fixed 

 structures, with a definite boundary, which has no tendency to become 

 diffuse or to spread outwards. There is thus a limit to the range of 

 action of the explosive corpuscles, and there is no evidence that, as 

 Hardy suggested, they yield a ferment which causes the plasma, as a 

 whole, to coagulate. 



On first formation, these localized coagula are plastic structures, 

 which can be modified in shape by movements of the surrounding fluid. 

 They are likewise sticky, and tend to adhere to or entangle any cells 

 with which they come in contact. They soon set and harden, however. 

 In a film that has been kept at rest their usual form is circular. The 



* Proc. Zool. Soc, 1909, pt. iv. (published 1910) pp. 848-79 (2 pis. and 2 figs.), 

 f Quart. Journ. Exper. Physiol., iii. (1910) pp. 1-20. 



