MORPHOLOGY OP THE PEDIPALPI. 33 



ventral part of the first two being much smaller than the dorsal. 

 They are placed in front of the first dorso-ventral muscle (i. e. the 

 muscle of the second segment), and between the first and second, 

 and the second and third dorso-ventral muscles respectively. The 

 fourth diverticulum is very much larger than the others, and 

 runs back along each side of the gut, somewhat dorsal to it. It 

 opens into four secondary lobes on the ventral side, lying in the 

 4th, 5th, 6th, and 7th segments respectively, and is continued, 

 though much reduced in size, as far as the postej'ior end of the 

 body. 



Behind this middle section of the mesenteron comes a con- 

 siderable length of narrow intestine, which expands about the 

 seventh segment into a great oval stercoral pocket which reaches 

 to the posterior end of the body. This stercoral pouch is in 

 absolute continuity with the rest of the gut, and is, I have no 

 doubt, derived from the hypoblast. 



The proctodseum consists of a solid mass of cells, which comes 

 into contact with the closed posterior end of the stercoral pocket. 

 The cells are, however, quite diff'erent in appearance from those 

 lining the stercoral pocket, and though in contact, the line of 

 demarcation is perfectly distinct. 



The Nervous System. 

 I have been able to make out but little as regards the develop- 

 ment of the nervous system, as in my younger stage it is practically 

 fully formed, though, as is usually the case wdth embryos, far 

 larger in proportion than in the adult. The ganglion for the 

 chelicerse is quite distinct from the brain in my embryos. Gan- 

 glion, by the way, used in this sense has exactly the opposite 

 meaning to that in Vertebrata. In the latter it means a collection 

 of nerve-cells, while in the Arthropod cephalothoracic nervous 

 system it means a mass of white substance among the nerve-cells. 

 Behind the ganglion for the chelicerse are five, somewhat larger 

 similar ganglia appertaining to the five other appendages. Then 

 come six very small separate masses of white substance, and 

 finally a single elongated mass from which the nerve-cord runs 

 out. I have not found in these stages any distinct division of 

 the cerebral ganglion into three, such as has been described 

 for Limidus * and Spiders. The distinction between the cells 

 formiug the dorsal mass of the cerebral ganglion and those lying 



* Patten, Q. J. M. S. vol. xxxv. 

 LINN. JOUBN. — ZOOLOGY, VOL. XXV. 3 



