OF OECANTHUS AND TELEAS. 



267 



the cuticula which it has secreted, is at this time very thick, but as 

 the embryo increases in size it becomes proportionately somewhat 

 thinner and differentiated into a " ventral stripe." Subsequently 

 there is separated from the posterior end of the ventral stripe a mass 

 of cells which comes to lie dorsad to the stripe and posterior to the 

 mesenteron, to which latter it is intimately connected. Lying on 

 either side of the mesenteron but connected with its walls are seen 

 two elongated sacs (pi. 24, figs. 9, 11) terminating blindly at both 

 ends, which may be in some way related to the salivary glands of 

 the second larva. The motions of this larva are in the jjlane deter- 

 mined by the longitudinal and dorso-ventral axes of the body, with 

 the single exception of the lateral pair of mandibles, which move at 

 right angles to this plane. Immediately posterior to the mouth open- 

 ing are seen (pi. 24, fig. 6) two roughened patches of the cuticula 

 which will be seen further developed in the second larva. The larva 

 changes its position in the yolk by movements of the rows of 

 bristles after the manner of fins, by the flexion of the tail, and by 

 bending the entire body. Upon straightening out after having thus 

 flexed itself, it is propelled into new feeding grounds. At this sta"-e 

 the food consists of the yellow fat globules of the yolk. The color- 

 less amoeboid cells and albuminoid masses seem to remain undisturbed 

 by the parasite. In the act of deglutition the whole enteric cavity is 

 thrown into a series of contractions and peristaltic movements, 

 although no muscular elements are to be detected in the wall of the 

 mesenteron. 



The second larval stage is characterized by the peculiar form of the body, which strongly 

 resembles the cyclops larva of Ganin ; it is indeed equivalent to this stage in the scale of 

 development. It is mainly distinguished from the previous stage by the presence of two 

 hooked mandibles and a complicated apparatus functioning as lower lip. The changes occur- 

 ring in the spindle-shaped larva during the period of transition into the cyclops form have not 

 been observed ; however, I have not the slightest doubt that the latter is but the former in 

 a later stage of development. In a series of Oecanthus eggs taken from the same elder stem, 

 eighteen out of twenty-five were infested with the parasite. Several of these contained the 

 three stages that I have described as belonging to one species of Teleas, a greater number 

 enclosed both the cylindrical and the cyclops forms, but by far the majority of the eggs 

 contained two or more cyclops larvae. In those eggs in which the cylindrical larva is 

 found, I have never observed more than one cyclops larva. These facts indicate that the 

 ova of the parasite had been deposited in varying numbers in the eggs of Oecanthus and 

 that of the forms developed from these, some were retarded in their growth. 



In this stage the cuticular secretion is highly differentiated, the complications of its 

 structure increasing with each ecdysis. During the period of transition from the first to 

 the second larval stages, the form of the body undergoes such marked changes that the 

 latter bears but little resemblance to the spindle-shaped larva. The cyclops larva is 

 about 0.5 m.m. in length. PI. 24, figs. 19-23, and pi. 25, figs. 1, 7, give one a clearer 



Fig. 38. Fig. 39. 



Fig. 38. Side view of cau- 

 dal spines showing graded va- 

 riations in the number and 

 position of the stout basal 

 spines. X 125. 



Fig. 39. Two bristles from 

 the dorsum of the same indi- 

 vidual. They appear filled 

 with a granular protoplasm- 

 Osmic acid preparation. X 

 800. 



