TRANSACTIONS OF SECTION D. GOB 



Hei-mit Crabs {Soldier Crabs).--7. Cccnohita rugosus, grey or lilac in colour, 

 of small size, and numerous along the shore. 



8. Cmnobita perlatii.f:, scarlet and white in colour, of middle size, and also 

 found chiefly near the shore. 



9. Ccunobita di/ptatiis, purple in colour, of large size, and "found in the jungle. 

 Slaters (Isopoch) : — 10. Cuharis muriuiis, and 11, P/tiloscia sp., woodlice. 



12. Ligia exotica, lives on the shore. 



Land crustaceans, which are the dominant group in a coral island, are of im- 

 portance in the economy of the island : 



i. As scavengers. 



ii. In the destruction and disintegration of fruits. 



iii. In the distribution of seeds. 



iv. In the same manner as earthworms by their burrowing. 



V. As enemies of various animals. 



vi. Occasionally as food for other animals. 



vii. Possibly in the fertilisation of flowers. 



viii. Probably in many other ways as yet unknown. 



3. On the A natomy of the Larval Polypterus. 

 Sy J . S. BuDGETT, M.A., Trinity College, Cambridge. 



The material for this paper is furnished by a single example of a larval Poly- 

 pterus, obtained in the Gambia in 1900. 



The larva measures 30 mm. in length, and is in the condition when the 

 cartilaginous skeleton has reached its highest development and ossification is 

 about to commence. 



The structure of the pectoral fins at this stage affords a strong argument in 

 favour of the view that the Crossopterygian fin is derived from the uniserial type 

 of fin and not from the biserial archipterygium. The suspension of the jaws is 

 in a primitively hyostylic condition, while the hyomandibular cartilage carries a 

 segmented rod of cartilage forming the axis of the root of the external "-ill. 



The vertebral cartilages resemble in their mode of formation those of 

 Lepidosteans and Teleosteans but, in addition to neural and hasmal cartilages to 

 each segment, there are distinct lateral cartilages. The haemal cartilages give 

 rise to the ventral ribs, which are thus shown to be homologous with the ribs of 

 other Ganoids and Teleosteans, while the lateral cartilages give i-ise to the trans- 

 verse processes and lateral ribs, which are homologous with those of Elasmo- 

 branchs, Amphibians, and Amniota. 



The oviducts are formed by the folding oflT of a portion of the body cavity 

 into which open a number of nephrostomes, and are thus shown to be of a nature 

 quite diiferent from true Midlerian ducts ; there is some evidence that the corre- 

 sponding duct in the male is homologous with the longitudinal canal of the 

 testicular network in those forms which have vasa efi'erentia passing to the 

 kidneys, while the vasa efi'erentia themselves are modified nephrostomes. The 

 head kidney is a very large organ lying between the foremost dorso-lateral and 

 ventro-lateral muscles far from the middle line : it consists of the much coiled 

 anterior end of the archinephric duct, and ends opposite a rather small glomus lyino- 

 close to the aorta, in the pronephric chamber, which is apparently without a 

 funnel, passing to the general body cavity. 



The structure of this larva confirms the belief that Polypterus is an extremely 

 generalised creature showing affinities with three great divisions of Ichthyopsida 

 Teleostei, Elasmobranchi, and Amphibia. ' 



4. The Origin of the Paired Limbs of Vertebrates. 

 By J. Gbaham Kerr. 



_ The author gave a short account of his hypothesis as to the phyloo-enetic 

 origin of the paired limbs of vertebrates. He passed in review the two current 

 1901. ^ ^ 



