164 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Ckelonians, Lacertilians, and Ophidians. He gives a useful summary 

 of fifteen chief conclusions, but our space will not admit of more than 

 a reference to a few. The development of the alimentary muscular- 

 layers is at its minimum in snakes, which may be associated with the 

 strong muscularity of the body-wall. In most cases there is no basal 

 membrane beneath the epithelium ; there are no cell-walls, but there is 

 often intercellular substance, and there may be intercellular bridges. 

 The oesophageal mucosa shows interesting stages of differentiation from 

 ciliary to stratified epithelium. (Esophageal glands occur in some 

 Chelonians. The gastric glands are very deep in Chelonians, deep in 

 lacertiform lizards, much less deep in serpentiform lizards and in snakes. 

 In the mid-intestine there is a lining of cylindrical cells with plasmio 

 prolongations differentiated into rods and with a small quantity of 

 intercalary substance. These rods exhibit pseudopodial movements, and 

 ingest like Amcebse. Cylindrical and calyciform cells in the intestine 

 are usually the same elements at two stages. Beguin pays particular 

 attention to the glandular cells of the stomach. 



Structure of Intestinal Villi.* — F. Vosselerhas studied the villi of 

 the small intestine in many animals, and he calls attention to numerous 

 peculiarities of structure. Thus he has found that, quite apart from results 

 of injury or degeneration, the villus may show an opening at or soine- 

 Avhat lateral to its apex. Sometimes two are present. They are elongated 

 clefts, bordered by cylindrical epithelium, and with the margins all but 

 touching. Not infrequently the stroma of the apical region of the villus 

 is cleanly retracted from the enveloping epithelium, so that between the. 

 two tissues there is a cap-shaped or cylindrical cavity containing some 

 granular debris and leucocytes, but without any formed fibrous com- 

 ponents. Vosseler considers the possible physiological import of the 

 structural facts described. 



So-called " Telescopic " Eye of Some Abyssal Fishes. | — A. Brauer 

 describes a kind of eye that frequently occurs in deep-sea fishes and in 

 some pelagic forms as well. He refers to some interesting cases in which 

 incipient stages towards the so-called telescopic eye occur. 



The chief characteristics of the peculiar type of eye alluded to may 

 be summed up as follows. The form is more or less like a tube, its. 

 opening — the pupil — is always very wide, the iris is almost degenerate. 

 The pupil is usually quite filled by a large lens, which is over-arched by 

 a very convex cornea. Even more peculiar is the fact that the retina is 

 divisible into two parts which are dissimilar in their differentiation. The 

 large part— the main retina — lines the whole back of the eye, is usually 

 homogeneous, and is always highly developed. It is marked by the great 

 length and large number of the rods, many of which are unusually far 

 from the lens because of the elongation of the region between the cornea 

 and the back of the eye. The smaller part of the retina {Nebenretina) 

 usually occurs on the median wall of the eye, and is in various degrees 

 reduced when compared with the main-retina. The layers are thinner ; 

 the percipient elements, when present, are less numerous, shorter, and 



* Verb. Deut&cli. Zool. Ges., xii. Vers. (193?) pp. 203-13 (4 figs.). 

 t Tom. cit., pp. 42-57 (7 fig.-.). 



