74 



the whole interior of the body. It has, in fact, had all the trouble 

 of evolving from the primitive Metazoic type only to find that it 

 might have just as well remained in its original lowly condition 

 for all the good that its highly developed structures have been to 

 it. This species is an example of the very interesting zoological 

 phenomenon of " protandrous hermaphroditism," the animal 

 being first an active male and afterwards a sedentary female. In 

 other words the male is simply a larval stage of the female, pre- 

 senting many of the original characters possessed by the Isopod 

 before it fell into its debasing parasitic mode of living. This con- 

 dition is found in very few animals and presents to the student of 

 sex many interesting and intricate problems of wide application. 

 The male, or late larval stage, of Ciypeoniscus is much smaller 

 than the female, being only about one millimetre in length : it 

 shows many signs of degeneration for it has lost its eyes, its 

 mouthparts are reduced to a mere oval cone, and its antennae 

 function as grasping organs — being flattened and provided with 

 large teeth with wh : ch to hold on to its wife — but it still retains 

 the majority of its appendages, and is evidently capable, to some 

 extent, of an independent and active existence, though to a much 

 less degree than are most of the members of its family, the 

 Cryptoniscidae. Unfortunately, I have so far been able to pro- 

 cure only one specimen of each sex, although I have no doubt that 

 a little search among the mussels on Boscombe Pier would result 

 in the capture of further examples. The female which I have was 

 full of half-developed embryos, but these do not show the peculiar 

 plate covering the underside of the abdomen, which is found in 

 the larvae of this species and from which the genus takes its 

 name. The Idotea which had the misfortune to have its internal 

 arrangements disturbed by this strange pair had turned quite 

 yellow, though what was the cause of this coloration I could 

 not say: probably the damage done to the creature's anatomy by 

 the parasites affected its power of colour-secretion. 



Another Isopod new to the British Fauna which I took last 

 year is Heterotanais Oerstedi (Kroyer), a species belonging to the 

 very aberrant group Chelifera. These Isopods — if indeed they 

 should be classified among the Isopoda at all — are well distin- 

 guished by their lobster-like pincers and by various other anatom- 

 ical features: they are represented in this district by Apseudes 

 Latreilli, Tanais tomentosus, Leptochelia Savignyi, and this 

 species. I have found Heterotanais very plentifully in Christ- 

 church Harbour among the mud and algae on the surface of the 

 stones lying in the shallow water near the shore, where it may 

 eas : ly be picked out on account of its white colour. It is about 

 three millimetres in length and the male is remarkable for the 

 extraordinary size of its pincers or chelae, which seem out of all 

 proportion to the size of the poor little creature which has to carry 

 them about with it : they are imperfectly chelate and the thumb 

 consists of quite a thin plate so that it is somewhat difficult to 

 see of what service these appendages can be to this tiny quaint- 



