178 DESCRIPTIONS OF PREPARATIONS. 



commissures lies above the sternal elements of the various somites, the 

 heart beneath the central area of the omostegite, whilst the reproductive 

 anjd digestive organs occupy a position midway. The appendages of the 

 right side are left in situ. The modified first and second pairs of abdominal 

 limbs show that the specimen belongs to the male sex. 



The supra-oesophageal and twelve post-oral ganglia, six thoracic and 

 six abdominal, are seen in profile. The great length of the commissures 

 between the first-named ganglion and the first of the post-oral series or 

 infra-oesophageal ganglion, whence the six pairs of appendages connected 

 with the mouth are innervated, may be noted as corresponding with the 

 elongated antennary sternum. In the abdominal series a slip of blue paper 

 has been placed beneath the commissures uniting the fifth to the sixth 

 ganglion. A white bristle has been introduced through the mouth into the 

 oesophagus and stomach. This latter organ is large and extends forwards 

 behind the eyes, but its anterior wall has been displaced a little backwards. 

 It is divisible into a larger cardiac and a smaller pyloric portion, the pyloric 

 situate just in front of a piece of blue paper placed under the hepatic artery. 

 The lower edges of the liver lobes of the right side may be seen below the 

 posterior cardiac region and extending backwards below the commence- 

 ment of the intestine. The aperture of the common duct of the left liver 

 lobes lies at the apparent termination of the hepatic artery, a projection 

 in front of it marking the so-called pylorus. The part of the digestive tract 

 into which the liver ducts open constitutes the mesenteron, and represents 

 the archenteron of the embryo. The oesophagus and stomach are differen- 

 tiations of the stomodaeum, whilst the intestine, which runs straight to the 

 anus on the ventral surface of the telson, and is of great relative length, is 

 formed from the proctodaeum of the embryo. The mesenteron and its 

 appended glands are lined by endoderm, the oesophagus, stomach and 

 intestine by ectoderm which secretes a chitinous cuticle. This cuticle is 

 cast by the animal whenever it moults. 



The heart is a rounded body lying below the cardiac area of the 

 omostegite. Of the arteries, to which it gives origin, the left hepatic passes 

 obliquely downwards in front to gain the liver lobes, the sternal artery 

 obliquely downwards behind to pass between the commissures uniting the 

 third and fourth thoracic ganglia. Both these arteries have pieces of blue 

 paper placed beneath them. Another piece of blue paper has been placed 

 under the superior abdominal artery in the region of the fourth ab- 

 dominal tergum. The left anterior lobe of the testis lies below and in 

 front of the heart : the posterior azygos lobe beneath and behind it, 

 whilst numerous coils of the right vas deferens come into view between 

 the testis and intestine. The powerful and complex flexor muscle of 

 the abdomen may be seen below the intestine and above the nerve chain 

 extending into the thorax to be attached to the endophragmal skeleton (see 



