ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 461 



lympliatic spaces. These lacunee are found throughout the whole of 

 the body and contain very small corpuscles ; as they surround the 

 enlarged extremities of the water-tubes the connection between the 

 two is effected by the orifices in these latter, and the author has been 

 able to see the corpuscles entering the tubes from the lacunae. The 

 lymph-spaces are regarded as the indications of a rudimentary coelom. 



Observations on the Orthonectida.*— Elias Metschnikoff describes 

 a species which he found in Nemertes lacteus, where it forms under the 

 skin a large number of rounded, pyriform, or irregular bodies, 

 collected about the middle of the body only ; their presence would 

 appear to be the cause of the destruction of the generative organs of 

 their host. In size they vary from • 08 mm. to • 2 mm., and the latter 

 represent protoplasmic tubes in the interior of which there are a 

 number of embryonic and mature Orthonectids. There are male, 

 female, and hermaphrodite tubes, and the number of specimens found in 

 one tube varies considerably. The larger forms, which have a close 

 resemblance to the parasites figured by Keferstein and M'Intosh, are 

 dark grey or dark brown by reflected light. Non-granular trans- 

 parent lines give distinct indications of a segmentation, and in well- 

 preserved examples nine segments can be made out. The whole of 

 the upper surface is invested by delicate long cilia, which have a 

 locomotor function ; they fall off if the creature is kept for some time 

 in sea-water. When treated with salt solution of a medium strength, 

 and by sections prepared by Kleinenberg's method, and stained with 

 borax and carmine, the following points may be made out. 



There is an epidermic layer of a single set of cells, the constituents 

 of which are generally cuboid in form and are richly granular ; the 

 cells bounding the segments have few granules and are broadened out. 

 At the anterior pole of the body, and beneath the epidermis, there is 

 an aggregation of small cells, which appears to represent the rudiment 

 of some organ. The greater part of the body, that is the whole of 

 its internal contents, consists of proportionately large cells, polygonal 

 in form, with finely granular contents, and large round nuclei. 



The smaller kinds have the posterior end rapidly tapering, and 

 appear to move much more rapidly than the larger ; there are at least 

 eight ectodermal segments ; in these, which are the males, the struc- 

 ture of the epidermis is more difficult to make out than in the larger 

 females ; numerous granules are to be found in it. The cells of the 

 fourth segment are very long and extremely delicate. The interior 

 of the body contains an oval sac, which extends from the thii'd to the 

 fifth segment, and is filled with small bodies, which seem to be 

 zoosperms. 



Some embryonic stages were observed ; the youngest were seen to 

 be rounded or oval cell-aggregates, the constituents of which were of 

 two sizes ; they appeared to form a solid morula, without any signs 

 of a segmentation cavity, although such a cavity has, on previous 

 occasions, been observed. 



Nor has the author been able to make out the final fate of these 



♦ Zeitschr. f. wiss. Zool., xxxv. (1881) pp. 282-304 (1 pi.). 

 Ser. 2.-YOL. I. 2 I 



