226 SUMMARY OF CURRENT RESEARCHES RELATING TO 



point out that, thougli most plumicolous Sarcoptids are oviparous, some 

 are viviparous (e. g. Fryana) ; the covering of the egg is sometimes 

 tubercular and sculptured, and in Analges fuscus has a double row of 

 cells, comparable to the ring of certain sporangia, and forming an 

 organ of dehiscence. The dorsal tegumentary plates are not always 

 granular, as in the species studied by Eobin ; they are often per- 

 forated or reticulated. The nymphs are sometimes found under two 

 forms, which differ in size. The curious red-coloured vesicles which 

 are found on the flanks of a species of Pterolichus may be regarded as 

 secondary sexual organs ; the female has two, the male one pair. 

 When highly magnified they have the appearance of a flattened 

 uniform plate, formed of a large number of tubes which open into an 

 excretory canal, the orifice of which is lateral or posterior. The red 

 colour is due to a liquid which fills the tubules. They appear to be 

 modified segmental organs, but their function is still unknown. 



5. Crustacea. 



Sexual Characters of Limulus.* — B. F. Koons has been puzzled 

 by the fact that no cast-off shells of Limulus bearing the characteristic 

 modified claw of the male have been found ; he now sees that this is 

 to be explained by the young male having the claws of the second pair 

 of appendages similar to those of the female ; as no large exuvise have 

 been found it is probable that the fully grown Limulus does not shed 

 his integument. Howsoever young specimens may be, the sexes are 

 to be distinguished by the transverse slits of the oviducts, and the 

 papillae with terminal circular orifices in the male. Females are larger 

 than males, and the carapace of large specimens is overgrown with 

 alg89, and appears rusty and aged, while those of smaller examples 

 are bright and clean, pointing to their being frequently shed ; indeed 

 the covering appears to be shed several times during the first year. 

 While the entire length of the exuvia may be only 4'0 mm. the 

 escaped young measure 7 • 1 mm. : an exuvia of 7 • mm. has a naked 

 young of 10*7 mm., while when the shed integument is 29 mm. the 

 escaped young have been found to be as much as 40 mm. in length. 

 Corresjponding differences obtain in the different parts of the animal. 



Evidence of a Protozoea Stage in Crab Development.! — There 

 is great interest attached to speculations as to the probable ancestry 

 of the Decapods, owing to the value which the conclusions have in 

 enabling us to interpret palasontological facts. There have been quite 

 a number of theories advanced as to the original stem from which the 

 Decapods have been derived, two of which claim especial attention. 

 One is the theory of Miiller, who finds such a stem form in the zoea. 

 Another, suggested by Claus, or in a different form by Brooks, 

 considers the protozoea as the ancestral stem. It is of great im- 

 portance in understanding the Crustacea to decide between these two 

 views, inasmuch as by the first view Crustacea are supposed to have 

 descended from a form without a thorax, while according to the 



* Amer. Nat., xvii. (188:-5) pp. 1297-9. 



t Johns-Hopkins Univ. Circulars, iii, (1884) p. 41. 



