140 PROFESSOR E. RAY LANKESTER. 



trabeculae of the coxal gland (PI. XII, fig. 1, col). Its place in 

 Scorpio and in Limulus in relation to the coxal gland is taken 

 by another variety of connective tissue. It seetus that in the 

 coxal glands of Mygale the colloid substance with cells scat- 

 tered in it and widely separated from one another is entitled to 

 be regarded as a definite tissue, for which the name of '' dense 

 colloid tissue" may temporarily serve. It has a superficial 

 resemblance to the substance of foetal spongey bone formed 

 during ossification in cartilage. 



A pus. — Though the great development of the entosternite 

 is characteristic of the Arachnida, and is one of the common 

 features of structure which, as Straus Durkheim pointed out, 

 necessitates the placing of Limulus in the class Arachnida, I 

 have yet within the past few months discovered that structures 

 identical in form, position, and histological composition with 

 the Arachnidan entosternite exist in the Crustacea. 



The only well-marked separable entosternite which I have 

 at present found among Crustacea is inApuscancriformis 

 and Apus productus. The plate lies dorsal to the nerve- 

 cord below the alimentary tract in the mid line of the body 

 between the two great mandibles, some of the muscles of which 

 are inserted into it. It appears also to receive a muscle on 

 each side from the maxillae, and possibly some from the ventral 

 body wall. It is shown in PI. VIII, figs. 2 and 3, as separated 

 from its muscular attachments. A section showing the minute 

 structure drawn to the same scale as the sections of ento- 

 sternites on Plate VII is represented in PI. VIII, fig. 1. It 

 will be admitted at once that we have here a fibroid skeletal 

 tissue of exactly the same character as that presented by the 

 Arachnidan entosternite. 



Naturally one expects the tendinous rods and processes 

 within a Crustacean thorax to be inversions of the epidermal 

 cuticular system. That this entosternite of Apus is not so is 

 proved, firstly, by its want of any direct continuity with the 

 integument as detertnined by means of a series of transverse 

 sections of Apus, and secondly by its histological character. 

 The apodemes and chitinous ingrowths of the integument 



