100 Mr. H. J. Carter on Microscopic Filarida?. 



that affords a part of these organs distinctly, and none of them 

 the whole at once. 



In some instances, where the vulva is placed very far back, 

 the generative organs can hardly be assumed to be symmetrical, 

 as there is no room for an equal development of the posterior 

 half. 



In some, again, the ova undergo segmentation to such an 

 extent before being laid, that the young worm is perfectly 

 formed j but I have met with no instances in which it has left 

 the egg while in the interior, so as to make the species vivipa- 

 rous ; while in other species segmentation does not commence 

 until the ovum has been discharged, as in Urolabes palustris. 



Where I have had an opportunity of tracing the development 

 of the embryo, as in Urolabes crythrops, the yelk has undergone 

 the common duplicative subdivision already well known to take 

 place in the ovum of Ascaris, — the divisions being widely sepa- 

 rated at first, and then gradually becoming more approximated 

 as the segmentation increases, until the whole is again brought 

 together, as in the first instance, and the formation of the new 

 being is commenced. 



The breeding-season of Urolabes palustris appears to com- 

 mence in January or February, and is all over by the beginning 

 of May; at least, in this month, and during the "rains/' I 

 have never met with any females with eggs in them. That of 

 the salt-water species also appears to be chiefly in the spring ; 

 while that of the species which only appear during the " rains " 

 is of course confined to this period. 



Among the generic characters given by Dujardin to Rhabditis, 

 the narrow rigid tube, which appears to me to be the oesophagus, 

 is not mentioned, and the muscular sheath which I have de- 

 scribed is viewed alone as the oesophagus. Now, as before 

 stated, the former appears to me to be the oesophagus, for this 

 reason, that in Urolabes palustris, which is typical of all the rest 

 in this respect, I have seen oil-globules (the food) come out of 

 the pointed extremity of the oesophagus after its exsertion under 

 pressure, while no food ever appears outside this or in the mus- 

 cular sheath, and the narrow tube which is continued backwards 

 from the sharp point is the only part which is in continuation 

 with the intestine (PI. II. fig. 11 h, &c). Again, if the "top- 

 shaped stomach" of Dujardin be that globular portion which 

 appears just about the union of the intestine with the oesophagus 

 in Ascaris vermicular is, called also by Blanchard " ventricle or 

 stomach*," such a portion does not exist in all the Filaridse 

 that I have figured ; and where it does, the constriction which 

 forms this globular dilatation is in the sheath of the intestine 

 * Ann. des Sc. nat. t. xi. pi. 7. fig. 3 d (1849). 



