ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 227 



in tlie former case. In this case the minimum quantity of albumens 

 required must vary with the intensity of the labour. (5) An 

 organism which has ample means of subsistence, and is therefore 

 in a constant condition of efficiency, can utilize in profitable exer- 

 tions of strength more than half the latent force contained in the 

 digestible non-proteids supplied to it. 



Discrimination of Species. — In the introduction to his lately 

 published ' Pterophorid^ oi California and Oregon,' Lord Walsingham 

 observes : " The manner in which my journey was performed has 

 brought into some prominence the very interesting but perplexing 

 question of the value of apparently specific differences. In con- 

 sequence of my changing the collecting ground every two or three 

 days, with a few exceptions, throughout the season, by short marches 

 of from fifteen to thirty miles a day (moving northwards in the 

 summer of 1871 and southwards in the spring of 1872), I was enabled 

 to acquire a considerable series of specimens of several species, 

 ranging perhaps, in some instances, over 100 or 150 miles of country, 

 exhibiting almost imperceptibly gradual but extensive variation both 

 in size and colour. In one or two notable instances the range of this 

 variation would seem to include two or even three different forms, 

 which, if they had been found without their intermediate connecting- 

 links, would certainly have been considered distinct species ; and even 

 after a careful comparison of an extended series, it must still remain, 

 in some cases, an open question whether they are or are not entitled 

 to specific rank." 



B. INVERTEBRATA. 



MoUusca. 



Structure and Histology of the Ink-bag of Sepia.* — In Sepia 

 officinalis M. Girod finds the gland which secretes and the bag 

 which contains the ink to be quite distinct from each other. The 

 bag is formed of a wall made up of three coats; the external one 

 is formed by loose connective-tissue fibres ; the middle coat comprises 

 a layer of transverse and one of longitudinal muscular fibres and one 

 which imparts the silvery colour to the sac ; the interior coat consists 

 of a dense connective-tissue layer covered with a pigmented pavement- 

 epithelinm. At the posterior and inferior side the wall is invaginated 

 to receive the gland, which is immediately in contact with the internal 

 coat. The gland which is free and exposed to the water in front, 

 consists of areolcB formed by a number of undulating lamellae inserted 

 upon the wall and forming oblique and anastomosing septa or tra- 

 heculce across its cavity ; the septa are charged with black pigment. 

 But the essential part of the gland is an elongated conical body 

 occupying its lower third ; it is white at the apex, but towards its base 

 gradually assumes the appearance of the black trabeculee. The white 

 tissue of the apex is made up of elongated transparent cells, with a 

 large nucleus at one of their ends, resembling cylindrical epithelium ; 

 lower down in the cone the superficial cells vary from round to 



* Comptes Kenclus, xcii. (ISSl) pp. 364-7. 



