780 SUMMARY OF CURRENT RESEARCHES RELATING TO 



form of a sucker below. In it there arc threo vertical groups of 

 muscles, and a circular muscle. The muscular apparatus is more like 

 that of Lingula than of Crania ; the digestive organs are more com- 

 plicated than Owen thought : there is a vast ovoid stomach and a 

 largo liver. Tlio contral nervous system, though reduced, is more 

 easy to make out than that of Lingula or Crania. The genital organs 

 form two distinct groups, attached to the gastro-parietal and ilco- 

 parietal membranes ; the gonads are largo, and their branches aro 

 attached to an arborescent skeleton of connective tissue. The oviducts 

 arc formed by a pair of pleated funnels attached to the body-wall 

 and to the ilo (-parietal membrane ; they are continued forwards by a 

 long canal which is placed between the anterior adductors and the 

 body-wall, aud they open not far from the base of the arms. 



Structure of Lingula pyramidata.* — Dr. H. G. Beyer has pub- 

 lished an important memoir on this subject. 



The structure of the shell has been described by Gratiolct, who 

 rightly described it as being built up of alternating horny and cal- 

 careous layers : his " periostacum," however, is replaced by the name 

 " cuticle " ; this is continued over the whole surface of the shells and 

 the peduncle ; it remains unstained by borax-carmine, but is stained 

 variously by other agents. Just below the cuticle, as also in other 

 parts of the shell, are clusters, here and there, of small round homo- 

 geneous corpuscles, which are regarded as homologous, and perhaps 

 analogous, to those occurring in the septa, running vertically in tho 

 shell of Testicardinate Brachiopods. As the edge of the shell is 

 approached, the alternating calcareous and horny layers decrease in 

 thickness, and the horny layers are continued, below the epidermis of 

 the peduncle, as a " supporting lamella," which is acted on by staining 

 agents in exactly the same manner as are the horny layers. The 

 cuticle is probably a changed larval integument, or has in some way 

 been produced by it. The body-wall, mantle, and peduncle all have 

 the same structure, and consist of an ectodermic epithelium, a sup- 

 porting tissue, and a peritoneal epithelium ; all shell regions contain 

 prolongations of the body-cavity. The typical cuboidal character of 

 the ectoderm varies in different regions of the body : sometimes being 

 more than one layer in thickness, sometimes containing peculiar ovoid 

 bodies, somewhat like taste-bulbs. 



Immediately below the ectoderm the nervous system occurs in 

 certain regions ; as well as calcareous plates, which, when dissolved, 

 leave " vacuoles " surrounded by a membrane, together with nucleated 

 granular cells. The supporting lamella in those parts in which the 

 nervous system is found contains spindle-shaped nucleated cells. In 

 the peduncle and other regions, instead of a simple lamella of sup- 

 porting tissue, this becomes a network, in the meshes of which aro 

 bundles of spermatozoa. The bundles of fibres which pass to the 

 bases of " hair-follicles " near the margin of the mantle, and tho 

 " mesenteric bands," are not muscular, as has previously been stated 

 to bo the case, but are only bundles of this supporting tissue. All 



* Stud. Biol. Laborat. Johns-Hopkins Univ., iii. (ISfc6) pp. 227-60 (4 pis.). 



