61 



ACROCULIA. 



ACROGENS. 



Acrochordus Jaranicus. 



from others of the innoxious family of serpents by the innumerable 

 small scales which cover every part of the head and body both above 

 and below, and which in preserved specimens, or when the live 

 animal distends the 

 lungs and body with 

 air, assume the appear- 

 ance of so many granu- 

 lated warts or tuber- 

 cles. This circum- 

 stance has suggested 

 the name of Acrochor- 

 diis. The head of the 

 acrochord is flat, the 

 mouth is provided with 

 a double row of small 

 sharp teeth, but with- 

 out poison-fangs, and 

 the throat is capable of 

 enormous dilatation. 

 The tongue is short 

 and thick, the vent 

 simple and without the 

 horny spurs which are 

 common to many other 

 genera of serpents. 

 The only species of 

 which much is known 

 is the A crorlutrdtu 

 Jaranifux of Lacdpede 

 and others. This 

 animal averages from 

 six to ten feet in 

 length, and the body 

 grows gradually thicker 

 from the head to the 

 vent, and there sud- 

 denly contracts, so as to form a very short slender tail. In 

 the thickest part of the body, immediately above its junction 

 with the tail, the individual procured by Homstedt, of which 

 the entire length was eight feet three inches, measured three 

 inches in diameter, whilst the greatest breadth of the tail did not 

 exceed half an inch, and its length was scarcely a ninth part of 

 that of the whole body. This individual was a female, and, when 

 opened, was found to contain five young ones perfectly formed, 

 and about nine inches in length. It was caught in a plantation of 

 pepper-trees, and the Chinese, who accompanied Homstedt, cooked 

 and ate its flesh, and reported it to be of a most delicious flavour. 

 The stomach contained a quantity of half-digested fruit, from which 

 it has been inferred that this serpent is frugivorous. Cuvier, however, 

 doubts on this point. 



ACROCU'LIA, a fossil genus of Gatteropoda, allied to the Neritadaf. 

 It occurs in Palaeozoic strata. (Phillips.) 



A'CRODUS, a genus of fossil Placoid fishes, established by M. 

 Agassiz. The species occurs almost exclusively in the lias and oolite. 

 One British species (A. minimus) is referred to the keiiper series by M. 

 Agassiz. It occurs at Aust Cliff in the bone-bed. The others abound 

 at Lyme Regis, Bath, and Stonesfield. 



ACRO'GASTER, a fossil genus of fishes. (Agassiz.) 



ACROGENS (from tucpos, the topmost, and ytvvAu, to produce), in 

 Botany, one of the primary classes of the Vegetable Kingdom, according 

 to the Natural System. This class, with identical limits, is also known 

 by the following designations : 



. I 'iityledanf ( Jussieu), so named from the fact of the absence of 

 amongst this class of plants. 



/.' > > iiitiryonatce (Richard), designating the absence of any regular 

 embryo in the reproductive cells, or spores. 



Cellulara (De Candolle), denoting the general absence of vascular 

 tissue and the prevalence of cellular tissue in these plants. 



Agamce, of various authors, implying the absence of the necessity of 

 the union of two cells in order to reproduce a new individual. 



l'i-i//>i't;/iimia (Linnaeus), intended to convey the idea that if two 

 cells were necessary to the reproduction of the new plant in this class, 

 it was not obvious, as in the Pheenogamous plants. 



The Acroyeru, as equivalent to the above expression* for the same 



clam, embrace all those plants which are included in the above defi- 



H. This term itself is, however, only applicable literally to those 



plants which, destitute of flowers, possess a stem growing in a manner 



distinctive from those called Exogem [ExooENs] and Kndnijens 



\ KMIOOESS]. It has been thus restricted by Lindle^ in his ' Vegetable 



I urn,' and he places the stemless flowerless plants in another class, 



The structure of the stem, however, is at best an 



artificial character, and the adoption of the terms for the classes 



nive of its characters, has rather been accidental than necessary. 



On this account it is perhaps better to regard the Thallngtn as a 



n of Acrogem than an independent and equal group. 



Tins stems of Acrogeat differ much in appearance from those of 



in ;in.| Kmlogens. The wood is not secreted from layers of 



tissue, which have the power of reproducing regular zones of wood, 



as in Exogens, or a regular arrangement of vascular and cellular 

 tissue, as in Endogens. There is generally but a single ring of vascular 

 bundles even in the Ferns. These vascular bundles do not go on 



Chnoophora cxcelsa, an acrogcnous stem. 



increasing in size, but are all developed together. The lower part of 

 the stem does not continue to increase in size, and its growth is deter- 



Portton of outside of stem of (AiwqpAera cxcelsa, 



mined by the development of new vascular bundles in connection 

 with the leaves of the point or upper part of the stem : hence their 

 name. In the Liverworts and Mosses there is only a simple vascular 

 bundle in the centre of the stem. In Jsoetee too there is a ring of 

 vascular bundles. Science is very deficient in good observations on 

 the structure of the stems of these plants. 



The reproduction of the Acrogens is not so simple as was at one 

 time believed. The recent researches of Sumiuki, Hoflmeister, and 



